2.  NOUNS ENDING IN “O.”  If the final “o” is preceded by a vowel, the
   plural is formed regularly, i.e., by adding “s”:  as, cameo, cameos.  If
   the final “o” is preceded by a consonant, the tendency of modern usage
   is to form the plural by adding “es”:  as, hero, heroes; potato,
   potatoes.  The following common words, however, seem still to form the
   plural by adding “s” alone:—­

canto lasso proviso torso duodecimo memento quarto tyro halo octavo solo junto piano stiletto

3.  NOUNS ENDING IN “Y.”  If the “y” is preceded by a vowel, the plural
   is regular:  as, valley, valleys.

If the “y” is preceded by a consonant, “y” is changed to “i” and “es” is added to form the plural:  as, lady, ladies; city, cities.

4.  PROPER NOUNS are changed as little as possible:  as, Henry, Henrys;
   Mary, Marys; Cicero, Ciceros; Nero, Neros.
5.  Most COMPOUND NOUNS form the plural by adding the proper sign of the
   plural to the fundamental part of the word, i.e., to the part which
   is described by the rest of the phrase:  as, ox-cart, ox-carts;
   court-martial, courts-martial; aide-de-camp, aides-de-camp.

Note the difference between the plural and the possessive of compound nouns,—­forms which are often confounded.  See page 16.

6.  Letters, figures, and other symbols are made plural by adding an
   apostrophe and “s” (’s):  as, “There are more e’s than a’s
   in this word”; “Dot your i’s and cross your t’s.”

7.  Some nouns have two plurals, which differ in meaning:—­

Singular.  Plural.

brother          brothers (by birth), brethren (of a society).
die              dies (for coining or stamping), dice (for play).
fish             fishes (separate fish), fish (collective).
index            indexes (in books), indices (in algebra).
penny            pennies (separate coins), pence (sum of money).
shot             shots (discharges), shot (balls).
staff            staves (poles), staffs (bodies of assistants).

[15] “Foundations,” pp. 45-47.

EXERCISE XI.[16]

Write the plural of:  Lash, cage, race, buffalo, echo, canto, volcano, portfolio, ally, money, solo, memento, mosquito, bamboo, ditch, chimney, man, Norman,[17] Mussulman, city, negro, baby, calf, man-of-war, attorney, goose-quill, canon, quail, mystery, turkey, wife, body, snipe, knight-errant,[17] donkey, spoonful, aide-de-camp, Ottoman, commander-in-chief, major-general, pony, reply, talisman, court-martial, father-in-law, court-yard, man-trap, Brahman, journey, Henry, stepson, deer, mouthful, Miss Clark,[18] Mr. Jones, Dr. Brown, Dutchman, German, forget-me-not, poet-laureate, minister-plenipotentiary, hero, fish, trout, Mary, George, bill-of-fare.