Page 111 - Perfect English Grammar: The Indispensable Guide to Excellent Writing and Speaking

Biceps (the main muscle of the upper arm) is the same in both the singular and
plural, but a misunderstanding about this has gone on for so long that an

adjective bicep is now acceptable. The singular noun bicep is almost there, but
my advice is to stick to a singular biceps. The same goes for triceps and

quadriceps.
Gyro is now widely accepted as the singular word for the spiced-meat-on-

pita sandwich, but some sticklers may still be holding out for gyros, the original
singular and plural form. Pronunciation of the word is similarly confused, with

YEER-oh, GUY-roh, and JIE-roh all being widely used. The first is more
traditional; the last is most common.

Kudos is another Greek word whose ending is misunderstood and whose

widely used singular form, kudo, is a break from the past, when kudos was the
singular form.

Others that you can look up in a good dictionary: forceps, rabies, species.

8.6.5 APOSTROPHES DON’T MAKE WORDS PLURAL

Never use an apostrophe to make a word plural. A word gets an apostrophe only
if it is possessive. Even then, the apostrophe goes after the plural suffix, not

before it: the buses’ headlights the compact discs’ plastic cases

8.6.6 PLURALS OF SOME COMPOUND NOUNS

One unusual kind of plural is for some compounds that involve a noun followed
by an adjective (see section 11.0) or adjectival phrase. To make them plural, the

-s goes on the noun part of the compound, even though it’s not the last word.

Singular Plural Possessive

attorney-at-law attorneys-at-law attorney-at-law’s case

attorney general attorneys general attorney general’s
opinion

brother-in-law brothers-in-law brother-in-law’s baby