Page 549 - Practical English Usage 3ed - Michael Swan, Oxford

criterion diagnosis
formula fungus
hypothesis kibbutz nucleus
oasis phenomenon radius stimulus vertebra
criteria (Greek) diagnoses (Greek)
formulae (Latin) or formulas fungi (Latin) or funguses
hypotheses (Greek) kibbutzim (Hebrew) nuclei (Latin)
oases (Greek) phenomena (Greek) radii (Latin)
stimuli (Latin) vertebrae (Latin)
singular and plural (2): irregular and special plurals 524
Note that some foreign plurals (e.g. agenda, spaghetnl are singular in English (see 148.5).
5 plurals in's
An apostrophe (') is used before the -s in the plurals of letters of the alphabet, and sometimes in the plurals of dates and abbreviations.
She spelt 'necessary' with two c's.
[loved the 1960's. (the 1960s is more common) PC's are getting cheaper. (PCS is more common)
It is not correct to use -'s in other plurals, e.g. jean's.
6 compound nouns
In noun + adverb combinations, the plural -s is usually added to the noun.
Singular
passer-by runner-up
Plural
passers-by runners-up
The plural of mother-in-law and similar words is generally mothers-in-law etc, but some people use mother-in-laws etc; the plural of court martial
(= military court or military trial) is either courts martial (more formal) or court martials (less formal).
In noun + noun combinations, the first noun is usually singular in form even if the meaning is plural (e.g. shoe shop). There are some exceptions. (see 531).
7 plurals with no singular forms
Cattle is a plural word used to talk collectively about bulls, cows and calves; it has no singular, and cannot be used for counting individual animals (one cannot say, for instance, three cattle).
Many cattle are sufferingfrom a disease called BSE. (NOT ,oAI:te'h eaHie is ...) Police, staffand crew are generally used in the same way.
The poUce are lookingfor a fair-haired man in his twenties. (NOT The I'61iee is 16Bking ... OR >'1 I'6liee ...)
The staffare on strike. (BUT A member ofstaffsaid . .., NOT 24. SttlJf• ••) However numbers are sometimes used before these three words (e.g. four staff, six crew).
The expressions the British, the Dutch, the English, the French, the Irish, the Spanish and the Welsh (see 17.2) are also plural, with no singular forms. •
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