Medical terminology

In short

Medical terminology is the standard word-building system of clinical language: most terms are assembled from a Greek or Latin root (the body part), a prefix (position, number, negation) and a suffix (condition, procedure or specialty), joined by a combining vowel. For an allied health professional it is the working language of requisition slips, consent forms, OT notes, dialysis charts, spectacle prescriptions and radiology reports — misreading one term can mean the wrong side, wrong organ or wrong exposure factor. Every B.Sc Allied Health programme (Radiology/Imaging Technology, Operation Theatre Technology, Optometry, Renal Dialysis Technology) carries a first-year paper on medical terminology, and it recurs in anatomy, pathology and clinical-posting vivas. In placement tests at Apollo, Fortis, Max, Manipal, AIIMS, Tata Memorial, NephroPlus, DaVita, Lenskart and Titan Eyeplus, decoding terms, expanding abbreviations and matching procedure names to modalities are standard screening questions.

Explained

How a medical word is built

• Word root: core meaning, usually the organ or tissue — *cardi* (heart), *ren*/*nephr* (kidney), *oste* (bone), *ocul*/*ophthalm* (eye), *gastr* (stomach), *pneum*/*pulmon* (lung).
• Combining vowel: usually o, inserted to ease pronunciation — root + o = combining form (*cardi/o*, *nephr/o*, *radi/o*).
• Rule 1: keep the combining vowel when the suffix begins with a consonant — *nephr/o/pathy*, *cardi/o/megaly*.
• Rule 2: drop it when the suffix begins with a vowel — *nephr + itis = nephritis*, not nephroitis.
• Rule 3: keep the vowel between two roots even if the second starts with a vowel — *gastr/o/enteritis*, *oste/o/arthritis*.
• Prefix: goes in front, modifying — *hyper-*, *hypo-*, *peri-*, *endo-*, *dys-*, *a-/an-*, *poly-*, *brady-*, *tachy-*.
• Suffix: goes last and decides the word class — condition (*-itis*, *-osis*, *-algia*), procedure (*-ectomy*, *-scopy*, *-graphy*), specialist (*-logist*).
• Reading order: read the suffix first, then the prefix, then the root — *pericarditis* = inflammation (itis) around (peri) the heart (cardi).
• Many terms have Greek (clinical: *nephros*, *ophthalmos*) and Latin (anatomical: *ren*, *oculus*) pairs — hence *renal failure* but *nephrology*.

Prefixes and suffixes that are asked most

• Position/direction: *ab-* away, *ad-* toward, *epi-* upon, *sub-/infra-* below, *supra-* above, *inter-* between, *intra-* within, *trans-* across, *retro-* behind, *ante-/pre-* before, *post-* after, *circum-/peri-* around, *ecto-/exo-* outside, *endo-/intra-* inside.
• Number/size: *mono-/uni-* one, *bi-/di-* two, *tri-*, *quadri-*, *hemi-* half, *semi-* half, *poly-/multi-* many, *macro-* large, *micro-* small, *oligo-* scanty, *pan-* all.
• Negation/abnormality: *a-/an-* without, *anti-/contra-* against, *dys-* painful or faulty, *mal-* bad, *pseudo-* false, *hyper-* excess, *hypo-* deficient, *neo-* new, *dextro-* right, *sinistro-* left.
• Condition suffixes: *-itis* inflammation, *-osis* abnormal condition, *-oma* tumour, *-pathy* disease, *-algia/-dynia* pain, *-megaly* enlargement, *-sclerosis* hardening, *-stenosis* narrowing, *-ectasis* dilatation, *-ptosis* drooping, *-cele* hernia/swelling, *-rrhage/-rrhagia* bursting forth of blood, *-rrhoea* flow, *-rrhexis* rupture, *-emia* blood condition, *-uria* urine condition, *-penia* deficiency, *-cytosis* increase in cells, *-lysis* breakdown, *-malacia* softening, *-trophy* growth/nourishment, *-plasia* formation.
• Procedure suffixes: *-tomy* cutting/incision, *-ectomy* surgical removal, *-ostomy* creating an opening, *-plasty* surgical repair, *-pexy* fixation, *-desis* fusion, *-rrhaphy* suturing, *-centesis* puncture to aspirate, *-scopy* visual examination, *-graphy* process of recording, *-gram* the record, *-graph* the recording instrument, *-metry* measurement, *-therapy* treatment.
• The classic triad: *tracheotomy* (incision), *tracheostomy* (opening to the surface), *tracheectomy* (removal) — commonly asked in OT technology papers.
• Specialty/person: *-logy* study, *-logist* specialist, *-iatrics/-iatry* treatment, *-ician* trained person (*technician*), *-ist* practitioner (*optometrist*, *radiographer* is an exception).

Anatomical reference language

• Anatomical position: standing erect, eyes forward, arms at sides, palms facing forward, feet parallel — all directional terms assume it.
• Directional pairs: superior/inferior, anterior (ventral)/posterior (dorsal), medial/lateral, proximal/distal, superficial/deep, ipsilateral/contralateral, unilateral/bilateral.
• Planes: sagittal (divides left-right; mid-sagittal/median is central), coronal/frontal (anterior-posterior), transverse/axial/horizontal (upper-lower), oblique (any angled plane).
• Body cavities: cranial, spinal, thoracic (with mediastinum, pleural cavities), abdominal, pelvic; diaphragm separates thoracic from abdominal.
• Abdominal regions: nine regions (right/left hypochondriac, epigastric, right/left lumbar, umbilical, right/left iliac/inguinal, hypogastric) or four quadrants (RUQ, LUQ, RLQ, LLQ).
• Movements: flexion/extension, abduction/adduction, pronation/supination, inversion/eversion, rotation, circumduction, dorsiflexion/plantar flexion.
• Positions used in imaging and OT: supine, prone, lateral decubitus, erect/orthostatic, Trendelenburg (head down), reverse Trendelenburg, Fowler's/semi-Fowler's, lithotomy, Sims', lateral/jack-knife, recumbent, recumbent oblique.

Modality-specific vocabulary

• Radiology projection terms: AP (anteroposterior — beam enters anterior, exits posterior), PA, lateral, RAO/LAO/RPO/LPO (oblique, named by the body part closest to the image receptor/film in the posterior or anterior oblique sense), axial/tangential, decubitus.
• Radiology procedure terms: *radiography*, *fluoroscopy*, *tomography*, *angiography* (vessels), *arthrography* (joint), *myelography* (spinal cord/canal), *cholangiography* (bile ducts), *hysterosalpingography* (uterus and tubes), *urography/IVU* (urinary tract), *mammography*, *sialography* (salivary ducts), *venography*, *barium swallow/meal/enema*.
• Imaging descriptors: radiolucent (dark, low attenuation), radiopaque (white, high attenuation), hyperdense/hypodense (CT), hyperechoic/hypoechoic/anechoic (ultrasound), T1/T2 hyperintense (MRI), artefact, attenuation, contrast resolution, dose terms (gray Gy for absorbed dose, sievert Sv for effective dose, mGy·cm for DLP).
• Operation theatre terms: *asepsis*, *scrubbed/unscrubbed*, *sterile field*, *diathermy/electrocautery*, *haemostasis*, *laparotomy* vs *laparoscopy*, *anastomosis*, *biopsy* (*incisional*, *excisional*, *FNAC*), *intubation/extubation*, *anaesthesia* (general, regional, spinal, epidural, local), *analgesia*, *premedication*, *elective* vs *emergency*, *-plasty/-pexy/-rrhaphy* repairs, *pneumoperitoneum*.
• Optometry terms: *myopia*, *hypermetropia/hyperopia*, *astigmatism*, *presbyopia*, *anisometropia*, *amblyopia*, *emmetropia*, *ametropia*, *strabismus* (eso-/exo-/hyper-/hypotropia), *nystagmus*, *diplopia*, *keratometry*, *retinoscopy*, *perimetry*, *tonometry*, *pachymetry*, *keratoconus*, *pseudophakia*, *aphakia*, *mydriasis/miosis*, *OD* (right eye), *OS* (left eye), *OU* (both eyes), *sph/cyl/axis/add*, *PD* (interpupillary distance).
• Dialysis terms: *haemodialysis*, *peritoneal dialysis (CAPD/APD)*, *diffusion, convection, ultrafiltration, osmosis*, *dialysate*, *dialyser*, *AV fistula (AVF)*, *AV graft*, *CVC/tunnelled catheter*, *uraemia*, *azotaemia*, *oliguria/anuria/polyuria*, *haematuria*, *proteinuria*, *AKI*, *CKD*, *ESRD*, *dry weight*, *interdialytic weight gain*, *Kt/V*, *URR*, *disequilibrium syndrome*, *heparinisation*, *recirculation*, *priming*.

Abbreviations, symbols and records practice

• Clinical: Hx (history), Dx, Px (prognosis), Rx (prescription/treatment), Tx (treatment/transplant), Sx (symptoms/surgery), c/o (complains of), k/c/o (known case of), NAD (no abnormality detected), PTA (prior to admission).
• Vitals/labs: BP, PR, RR, SpO₂, Hb, TLC/DLC, RBS/FBS/PPBS, HbA1c, S. creatinine, BUN, eGFR, Na⁺/K⁺, LFT, RFT, ABG, ECG, TFT, INR.
• Prescription Latin: OD (once daily), BD/BID (twice), TDS/TID (thrice), QID, HS (at bedtime), SOS/PRN (as needed), stat (immediately), a.c./p.c. (before/after meals), PO (oral), IV, IM, SC, SL, NPO/nil by mouth.
• Beware of clashes: *OD* means "once daily" in prescriptions but "right eye" (oculus dexter) in ophthalmology, and "overdose" in emergency notes — context decides.
• Error-prone abbreviations: NABH-accredited Indian hospitals are required to maintain a hospital-approved abbreviation list and a "Do Not Use" list. Commonly banned items: U for units (read as 0 or 4), IU (read as IV), µg (write mcg), OD/QD (misread), trailing zero (write 1 mg, not 1.0 mg), missing leading zero (write 0.5 mg, not .5 mg), MgSO₄/MS/MSO₄ (write the drug name in full). Exact lists vary by hospital policy and NABH edition — follow the local approved list.
• Coding and classification: ICD-11 is the WHO classification in force since 1 January 2022 and is being adopted in India for morbidity and mortality coding; ICD-10 remains in use in many Indian records and insurance claims. ICD-11 TM-2 adds a traditional-medicine module relevant to Ayush. Procedure coding uses ICHI (WHO) or CPT where contracted; Indian insurance/PMJAY uses its own HBP (Health Benefit Package) procedure codes. SNOMED CT is licensed nationally in India through NRCeS/C-DAC for free use, and ABDM (Ayushman Bharat Digital Mission) mandates FHIR-based records with ICD-10/ICD-11 and SNOMED CT coding.

Spelling, plurals and pitfalls

• Latin/Greek plurals: -a → -ae (vertebra/vertebrae), -us → -i (bronchus/bronchi, nucleus/nuclei), -um → -a (ovum/ova, bacterium/bacteria), -is → -es (diagnosis/diagnoses, metastasis/metastases), -ix/-ex → -ices (apex/apices, appendix/appendices), -oma → -omata/-omas (carcinoma/carcinomata), -nx → -nges (phalanx/phalanges, larynx/larynges), -on → -a (ganglion/ganglia).
• Silent and soft letters: initial *pn-* (pneumonia), *ps-* (psychosis), *pt-* (ptosis), *rh-* (rhinitis), *x-* (xeroderma); *c* and *g* are soft before e, i, y (*cyst*, *gingiva*) and hard before a, o, u (*carcinoma*, *gastric*).
• Sound-alike traps: ilium (hip bone) vs ileum (small intestine); perineum vs peritoneum; mucus (noun) vs mucous (adjective); hypo- vs hyper-; dysphagia (swallowing) vs dysphasia (speech); prostate vs prostrate; aural vs oral; abduction vs adduction; arteriosclerosis vs atherosclerosis.
• Eponyms: named after people — Colles' fracture, Crohn's disease, Foley catheter, Fowler's position, Mayo stand, Snellen chart, Goldmann tonometer, Doppler, Bowman's capsule. They cannot be decoded by word parts and must be memorised.
• Acronyms vs initialisms: CABG and CAPD are pronounced as words; MRI and CKD are spelled out. Both are expanded in full at first use in a report.
• Standard practice in Indian hospital records: write the term in full the first time, keep the hospital abbreviation list, never invent abbreviations, and never use ditto marks or "same as above" in clinical entries.

Key points

• Word root - core meaning, almost always the body part or substance (nephr/o = kidney).
• Combining vowel - usually "o"; dropped before a vowel-starting suffix, kept before a consonant and between two roots.
• Reading order - suffix, then prefix, then root: *endocarditis* = inflammation within the heart.
• -tomy / -ostomy / -ectomy - cut into / make a permanent opening / cut out; the single most confused trio.
• -graphy / -gram / -graph - the process / the record / the machine; central to radiology vocabulary.
• -scopy vs -metry - looking at vs measuring (cystoscopy, perimetry).
• -centesis - puncture to withdraw fluid (thoracocentesis, paracentesis, amniocentesis).
• Hyper- vs hypo- - above vs below normal; a one-letter error reverses the clinical meaning.
• Anatomical position - erect, palms forward; every directional term is defined relative to it.
• Planes - sagittal (left-right), coronal (front-back), transverse/axial (top-bottom), oblique.
• AP vs PA - named by the direction the X-ray beam travels through the body, entry first.
• Radiolucent vs radiopaque - transmits X-rays (appears dark) vs absorbs them (appears white).
• OD ambiguity - right eye in ophthalmology, once daily in prescriptions; expand it in writing.
• Error-prone abbreviations - U, IU, µg, QD, trailing zeros are on typical "Do Not Use" lists under NABH policy.
• ICD-11 - WHO classification in force since 1 January 2022; ICD-10 still widely used in Indian records and claims.
• ABDM/SNOMED CT - digital health records in India use FHIR with SNOMED CT (licensed nationally via NRCeS) and ICD coding.
• Plurals - -is→-es, -um→-a, -us→-i, -a→-ae, -ix→-ices; wrong plurals lose marks in theory papers.
• Eponyms - cannot be decoded from word parts (Colles', Foley, Snellen, Fowler's) — learn them as names.

Formulas and examples

Medical terminology itself has no equations, but the clinical measures its vocabulary names are calculated as follows.

Example 1 — Decoding by word parts. Break down *pyelonephritis*, *oesophagogastroduodenoscopy*, *nephrolithotripsy*.

• *pyel/o* (renal pelvis) + *nephr* (kidney) + *-itis* → inflammation of the renal pelvis and kidney.
• *oesophag/o* + *gastr/o* + *duoden/o* + *-scopy* → visual examination of oesophagus, stomach and duodenum (OGD/EGD).
• *nephr/o* + *lith/o* (stone) + *-tripsy* (crushing) → crushing of a kidney stone.

Example 2 — URR for a dialysis chart. Pre-dialysis blood urea 120 mg/dL, post-dialysis 36 mg/dL.

• Drop = 120 − 36 = 84 mg/dL.
• URR = 84/120 × 100 = 70% — above the ≥ 65% target, so the session is adequate by URR.

Example 3 — Ultrafiltration order. Patient's dry weight 60 kg, pre-dialysis weight 62.4 kg, session 4 hours.

• Interdialytic gain = 62.4 − 60.0 = 2.4 kg → 2.4 L to remove.
• UF rate = 2,400 mL / 4 h = 600 mL/h; per kg = 600/60 = 10 mL/kg/h — at the upper end of the usually accepted range, so monitor for hypotension.

Example 4 — Spectacle prescription in words. OD −3.00 DS; OS −2.00 DS / −1.00 DC × 180; Add +2.00 DS.

• Right eye: 3.00 dioptres of myopia, spherical only.
• Left eye: myopic astigmatism — spherical equivalent = −2.00 + (−1.00/2) = −2.50 D.
• Add +2.00 D for near, indicating presbyopia; the spherical equivalents differ by only 0.50 D (−3.00 vs −2.50), so this is *not* significant *anisometropia*, which needs about ≥1 D difference between eyes.

Example 5 — Rewriting an unsafe order. "Inj. Lasix 20U IV QD, digoxin .25mg PO, MgSO4 1.0g IV stat."

• *20U* → write 20 mg (Lasix is dosed in mg; "U" is error-prone) ; *QD* → once daily.
• *.25mg* → 0.25 mg (add the leading zero); *1.0 g* → 1 g (drop the trailing zero).
• *MgSO4* → magnesium sulfate, spelled out.

Where it is used

• Radiology and imaging departments: reading requisitions, selecting the correct projection (AP, PA, RAO, decubitus), writing procedure names on CT/MRI/IVU/HSG worklists, and typing reports for radiologists at Apollo, Fortis, Max, AIIMS, Tata Memorial and district DH radiology units.
• Operation theatres and CSSD: understanding the surgical list (laparoscopic cholecystectomy, TURP, open reduction and internal fixation), setting instruments for the named procedure, positioning the patient (lithotomy, Trendelenburg) and documenting in the OT register and WHO surgical safety checklist.
• Dialysis units: charting pre/post weight, Kt/V, URR, access type (AVF/CVC), and reading nephrology notes at NephroPlus, DaVita, Apollo Dialysis and PMJAY-empanelled centres.
• Optometry and optical retail: transcribing sph/cyl/axis/add, OD/OS/OU, recording diagnoses such as keratoconus or amblyopia at Aravind, LVPEI, Sankara Nethralaya, Lenskart and Titan Eyeplus.
• Medical records, coding and insurance: ICD-11/ICD-10 coding, discharge summaries, PMJAY/HBP claims, TPA queries, and NABH documentation audits — a growing role for allied health graduates as medical coders and clinical documentation specialists.
• Health IT and transcription: ABDM/FHIR record systems, hospital HIS/RIS-PACS data entry, medical transcription and scribing for telemedicine providers.

Interview questions

• Q: What are the four word parts of a medical term? A: Prefix, word root, combining vowel (forming the combining form) and suffix; the root carries the core meaning and the suffix fixes the word's grammatical sense.
• Q: When do you keep the combining vowel? A: Keep it before a suffix starting with a consonant and between two roots; drop it before a suffix starting with a vowel — nephritis, not nephroitis.
• Q: Differentiate tracheotomy, tracheostomy and tracheectomy. A: Tracheotomy is an incision into the trachea, tracheostomy is creating an opening of the trachea onto the skin surface, and tracheectomy is surgical removal of part of the trachea.
• Q: What is the difference between -graphy, -gram and -graph? A: -graphy is the procedure of recording, -gram is the resulting image or record, and -graph is the instrument that records — angiography, angiogram, electrocardiograph.
• Q: What does AP projection mean and how does it differ from PA? A: The beam enters the anterior surface and exits the posterior in AP; in PA it enters posterior and exits anterior, with the anterior surface against the detector — a PA chest reduces heart magnification.
• Q: Radiolucent or radiopaque — which appears white on a radiograph? A: Radiopaque structures absorb X-rays and appear white; radiolucent structures transmit them and appear dark.
• Q: What does OD mean? A: It depends on context — *oculus dexter* (right eye) in ophthalmic notes, *omni die* (once daily) in prescriptions, and overdose in emergency notes, so it should be expanded in writing.
• Q: Give three abbreviations usually on a hospital's "Do Not Use" list and why. A: "U" for units (misread as 0 or 4), "IU" (misread as IV), and "QD"/"OD" for once daily (misread as QID); each has caused dosing errors, so hospitals under NABH keep an approved abbreviation list.
• Q: What is the plural of diagnosis, bronchus, vertebra and apex? A: Diagnoses, bronchi, vertebrae and apices.
• Q: Differentiate ilium and ileum, perineum and peritoneum. A: Ilium is the flared hip bone, ileum the last part of the small intestine; the perineum is the region between the anus and genitalia, the peritoneum the serous membrane lining the abdominal cavity.
• Q: An order reads "lithotripsy for nephrolithiasis" — decode it. A: *Nephr/o* kidney + *lith* stone + *-iasis* condition means kidney stones; *litho/tripsy* means crushing the stone, usually by extracorporeal shock waves (ESWL).
• Q: What is an eponym and why is it a problem? A: A term named after a person — Colles' fracture, Foley catheter, Snellen chart — which cannot be decoded from word parts and must be learnt by memory, and is often spelt or attributed wrongly.
• Q: Which classification is currently used for diseases, and what is India adopting? A: WHO's ICD-11 has been in force since 1 January 2022 and is being adopted in India, though ICD-10 remains common in records and insurance; digital records under ABDM also use SNOMED CT, licensed nationally through NRCeS.

Common mistakes

• Dropping or inserting the combining vowel wrongly — writing "nephroitis" or "cardiomegaly" as "cardimegaly".
• Confusing -tomy, -ostomy and -ectomy in exam answers, so the stated procedure is not the one asked.
• Swapping hyper-/hypo-, inter-/intra- or abduction/adduction — single-syllable errors that invert the clinical meaning.
• Using English plurals for Latin/Greek words (diagnosises, metastasises, bronchuses) and wrong spelling of silent-letter words (pnuemonia, tosis).
• Confusing AP with PA, or naming an oblique projection by the wrong side — leading to wrong marking and, in practice, repeat exposure.
• Inventing or copying unapproved abbreviations in case notes, and writing ".5 mg" or "1.0 mg" instead of "0.5 mg" and "1 mg".
• Treating eponyms as decodable (trying to break down "Colles'") or decoding abbreviations without checking context, as with OD.

Related topics

Human anatomy and physiology for allied health · Infection control and asepsis · Patient care, positioning and handling · Radiographic positioning and projections · Hospital records, ICD coding and health information management · Allied health careers and registration.