Medical Terminology For Dummies
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Medical plurals are a bit different from the standard, everyday English variety. There are a few rules that can help you derive a plural the medical way. Read on to familiarize yourself with the nuances of medical plural building.

Medical rules for forming plurals

Some rules for pluralizing medical terms are as follows, with examples of the rule and exceptions to the rule.

Medical Rule 1: Change the a ending to ae

In other words, vertebra becomes vertebrae.

By adding the e to the plural, the “aah” sound ending pronunciation becomes “eh.”

  • Axilla, axillae

  • Bursa, bursae

  • Conjunctiva, conjunctivae

  • Scapula, scapulae

  • Sclera, sclerae

Medical Rule 2: Change the um ending to a

The a at the end is pronounced “aah.”

  • Acetabulum, acetabula

  • Antrum, antra

  • Atrium, atria

  • Bacterium, bacteria

  • Diverticulum, diverticula

  • Labium, labia

  • Medium, media

Medical Rule 3: Change the us ending to i

The i at the end is pronounced “eye.”

  • Alveolus, alveoli

  • Bronchus, bronchi

  • Coccus, cocci

  • Embolus, emboli

  • Fungus, fungi

  • Glomerulus, glomeruli

  • Meniscus, menisci

  • Syllabus, syllabi (but syllabuses is also acceptable)

The exceptions to this rule include the following:

  • Corpus, corpora

  • Meatus, meatus (stays the same)

  • Plexus, plexuses

  • Viscus, viscera

Medical Rule 4: Change the is ending to es

The es is pronounced “eez.”

  • Analysis, analyses

  • Diagnosis, diagnoses

  • Exostosis, exostoses

  • Metastasis, metastases

  • Prognosis, prognoses

  • Testis, testes

The exceptions to this rule are

  • Epididymis, epididymides

  • Femur, femora

  • Iris, irides

Medical Rule 5: Change the ma or oma ending to mata

  • Carcinoma, carcinomata

  • Condyloma, condylomata

  • Fibroma, fibromata

  • Leiomyoma, leiomyomata

In the Rule 5 examples, the English plural is also acceptable: condylomas, carcinomas, leiomyomas, and fibromas.

Medical Rule 6: When a term ends in yx, ax, or ix, change the x to c and add es

  • Appendix, appendices

  • Calyx, calyces

  • Calix, calices (Strange but true, both are correct)

  • Thorax, thoraces

Medical Rule 7: When a term ends in nx, change the x to g and add es

  • Larynx, larynges

  • Phalanx, phalanges

Medical Rule 8: For Latin medical terms that consist of a noun and adjective, pluralize both terms

  • Condyloma acuminatum, condylomata acuminata

  • Placenta previa, placentae previae

  • Verruca vulgaris, verrucae vulgares

There are (of course!) some exceptions to all these rules:

  • Cornu, cornua

  • Pons, pontes

  • Vas, vasa

English rules of forming plurals

Many medical terms apply basic English rules for forming plurals. Thank goodness! You will no doubt recognize many of these common English language plural rules.

English Rule 1: Add an s

  • Bronchoscope, bronchoscopes

  • Disease, diseases

  • Endoscope, endoscopes

  • Finger, fingers

  • Vein, veins

English Rule 2: When a term ends in s, x, ch, or sh, add es

  • Crutch, crutches

  • Distress, distresses

  • Patch, patches

  • Stress, stresses

English Rule 3: When a term ends in y after a consonant, change the y to i and add es

  • Artery, arteries

  • Bronchoscopy, bronchoscopies

  • Endoscopy, endoscopies

  • Ovary, ovaries

  • Therapy, therapies

English Rule 4: When a term ends in o after a consonant, add nes

  • Comedo, comedones


  • Embryo, embryos

  • Placebo, placebos

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