Loans of Greek origin
-is [is] -es [i:z]
synopsis (резюме) synopses
ellipsis (эллипсис, лингв.) ellipses
-on [an] -a [э]
Loans of Latin origin
-us [эs] -i [ai]
corpus (свод, кодекс) corpora
genus (сорт) genera
fungus (низший гриб) fungi
genius genii (духи), geniuses (гении)
alumnus (бывший ученик, студент) alumni
-a [э] - ae [i:]
formula formulae (but – formulas of politeness)
vertebra (позвонок) vertebrae
-um [эm] -а[э]
datum (данные) data
stratum (пласт, слой) strata
erratum (опечатка) errata
addendum (приложение, дополнение) addenda
stadium stadia (or stadiums)
-es, -ix [iks] -ices [isi:z]
matrix (матрица) matrices
Plural of compound nouns
1. As a rule in compounds it is the second component that takes
housewives, tooth-brushes, boy-scouts, maid-servants, stepmothers, boyfriends
2. Compounds in -ful have the plural ending at the end of the word:
handfuls, spoonfuls, mouthfuls, (though spoonsful and mouthsful are also possible).
3. Compounds in which the first component is man or woman have
men-servants, women-doctors, gentlemen-farmers
But: man-eaters, lady-killers, man-haters, lady-birds
4. Compounds ending in -man change it into -men in spelling. In
policeman [эn] - policemen [эn].
Such nouns as German, Roman, Norman are not compounds, and therefore they have regular plurals:
Germans, Romans, Normans.
5. In compounds originating from a prepositional noun phrase where
editors-in-chief, mothers-in-law, commanders-in-chief, men-of-war (военные корабли).
6. In compounds with a conjunction as a linking element the plural is
7. In compound nouns formed by a noun plus a preposition, or an adverb
passers-by, lookers-on, courts-martial, attorneys-general (генеральный прокурор), by-standers (свидетели), hangers-on (прихлебатели)
8. When the compound is a substantivized phrase which does not
forget-me-nots, breakdowns, stand-bys, grown-ups, close-ups, pick-ups (случайные знакомства), drop-outs (дезертиры), go-betweens (посредники), good-for-nothings.
THE NOUNS FRUIT AND FISH
This noun is uncountable when it is used in the general meaning:
The fruit is not ripe yet.
There is fruit for dessert.
This noun is used as a class countable noun when it denotes different sorts of fruit:
There were different fruits on the table: apples, pears, plums.
A fruit – плод, сорт фруктов
A pear is a juicy fruit.
The fruits of labour.
This noun is uncountable when it denotes food:
I like fish for breakfast.
There is much fish on the plate.
This noun can also be used as a countable noun when it denotes live fish; in this case it has the identical form for the singular and the plural:
A fish – five fish, many fish
I’ve caught five big fish.
Fish don’t live without water.
The form fishes is used to denote different sorts of fish:
I have bought a book on fresh-water fishes.
Invariable nouns cannot change their number, some of them are always singular in meaning, some denote plurality.