12. Number is that quality of a word which shows whether it refers to one or to more than one. Singular Number refers to one. Plural Number refers to more than one.
13. Plurals of singular nouns are formed according to the following rules:
1. Most nouns add s to the singular; as, boy, boys; stove, stoves.
2. Nouns ending in s, ch, sh, or x, add es to the singular; as, fox, foxes; wish, wishes; glass, glasses; coach, coaches.
3. Nouns ending in y preceded by a vowel (a, e, i, o, u) add s; as, valley, valleys, (soliloquy, soliloquies and colloquy, colloquies are exceptions). When y is preceded by a consonant (any letter other than a vowel), y is changed to i and es is added; as, army, armies; pony, ponies; sty, sties.
4. Most nouns ending in f or fe add s, as, scarf, scarfs; safe, safes. A few change f or fe to v and add es; as, wife, wives; self, selves. The others are: beef, calf, elf, half, leaf, loaf, sheaf, shelf, staff, thief, wharf, wolf, life. (Wharf has also a plural, wharfs.)
5. Most nouns ending in o add s; as, cameo, cameos. A number of nouns ending in o preceded by a consonant add es; as, volcano, volcanoes. The most important of the latter class are: buffalo, cargo, calico, echo, embargo, flamingo, hero, motto, mulatto, negro, potato, tomato, tornado, torpedo, veto.
6. Letters, figures, characters, etc., add the apostrophe and s ('s); as, 6's, c's, t's, that's.
7. The following common words always form their plurals in an irregular way; as, man, men; ox, oxen; goose, geese; woman, women; foot, feet; mouse, mice; child, children; tooth, teeth; louse, lice.
Compound Nouns are those formed by the union of two words, either two nouns or a noun joined to some descriptive word or phrase.