November 2026 - Plural Spellings Study Guide for nursing students in
Most plurals add s or es, but words ending in consonant-y change to ies, some ending in f change to ves, and irregulars change form entirely. Medical terms follow Latin and Greek patterns, and those are the ones a nursing exam asks about.
Try 4 short questions throughout this guide. Check each answer to learn from the explanation.
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The regular rules
Ending
Rule
Examples
Most words
Add s
chart → charts
s, x, z, ch, sh
Add es
box → boxes; dish → dishes
Consonant + y
Change y to ies
artery → arteries; injury → injuries
Vowel + y
Add s
day → days; x-ray → x-rays
f or fe
Often change to ves
shelf → shelves; knife → knives
Consonant + o
Usually es
potato → potatoes
The y rule turns on the letter before it. Artery has a consonant before the y, so it becomes arteries; x-ray has a vowel, so it becomes x-rays. Checking that one letter resolves most y-ending questions without any memorisation.
Medical plurals worth learning
These follow Latin and Greek patterns rather than English ones, and they appear constantly in nursing texts.
Singular
Plural
Pattern
nucleus
nuclei
-us → -i
bacterium
bacteria
-um → -a
diagnosis
diagnoses
-is → -es
vertebra
vertebrae
-a → -ae
phenomenon
phenomena
-on → -a
index
indices
-ex/-ix → -ices
fungus
fungi
-us → -i
prognosis
prognoses
-is → -es
Question 1 of 4
What is the plural of diagnosis?
Choose one answer, then check it.
View the Answer and Explanation
Correct answer: C. diagnoses
Words ending in -is take -es in the plural, giving diagnoses — the same pattern as prognosis and analysis. Adding an English ending to a Greek word produces the first option, which is never correct.
The irregulars
These change form or do not change at all, and there is no rule — only recognition.
Watch the singular.Bacteria and criteria are plurals — the singulars are bacterium and criterion, and using the plural as a singular is a common error the exam tests directly.
Question 2 of 4
What is the plural of therapy?
Choose one answer, then check it.
View the Answer and Explanation
Correct answer: B. therapies
The letter before the y is a consonant, so it changes to ies. A vowel before the y — as in x-ray — would mean simply adding s instead, which is why checking that one letter matters.
Working out an unfamiliar plural
Worked example
What is the plural of biopsy?
Identify the ending: it ends in y.
Check the letter before the y: s, a consonant.
Consonant plus y means the y changes to ies.
So the plural is biopsies.
Biopsies. The same rule handles artery → arteries, injury → injuries and therapy → therapies — one check on one letter.
Terms to know
Plural
The form of a noun meaning more than one.
Regular plural
One formed by adding s or es.
Irregular plural
One that changes form or does not change at all.
Latin plural
A plural following Latin patterns: -us to -i, -um to -a, -a to -ae.
Greek plural
A plural following Greek patterns: -is to -es, -on to -a.
Collective noun
A word for a group treated as one thing, such as staff or team.
What the TEAS asks most
The same core ideas appear in different wording. If you can answer these without stopping to think, you have what this section requires.
What is the plural of this word?
Check the ending, then the letter before it. Medical terms usually follow Latin or Greek.
Which sentence uses the plural correctly?
Watch for a Latin plural used as a singular — one bacteria, one criteria.
Correct answer: B. A single bacterium was identified in the sample.
Bacteria is already plural, so a single organism is a bacterium — and a singular subject needs the singular verb "was". This mistake is so common in speech that recognising it in writing is exactly what the question tests.
Key points
Most nouns add s; those ending in s, x, z, ch or sh add es.
Consonant plus y becomes ies; vowel plus y just adds s.
Medical terms follow Latin and Greek patterns: nucleus/nuclei, diagnosis/diagnoses, vertebra/vertebrae.
Bacteria and criteria are plurals; the singulars are bacterium and criterion.
Some nouns — sheep, series, species — do not change at all.
Question 4 of 4
Which of these is the correct plural of vertebra?
Choose one answer, then check it.
View the Answer and Explanation
Correct answer: B. vertebrae
Latin words ending in -a take -ae, giving vertebrae. The -i ending belongs to words ending in -us, such as nucleus and fungus, and the English -s ending does not apply to this pattern.
TEAS · Plural spellings
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