I. s after a vȯiceless consonant, z after a vȯiced consonant or a vowel noun plural suffix
Etymology: Middle English -es, -s, from Old English -as, nominative & accusative plural ending of some masculine nouns; akin to Old Saxon -os
— used to form the plural of most nouns that do not end in s, z, sh, ch, or postconsonantal y
head s
book s
boy s
belief s
to form the plural of proper nouns that end in postconsonantal y
Mary s
and with or without a preceding apostrophe to form the plural of abbreviations, numbers, letters, and symbols used as nouns
MC s
PhD' s
4 s
the 1940' s
$ s
B' s
— compare -es I
II. adverb suffix
Etymology: Middle English -es, -s, plural ending of nouns, from -es, genitive singular ending of nouns (functioning adverbially), from Old English -es
— used to form adverbs denoting usual or repeated action or state
always at home Sunday s
morning s he stops by the newsstand
III. verb suffix
Etymology: Middle English (Northern & North Midland dialect) -es, from Old English (Northumbrian dialect) -es, -as, probably from Old English -es, -as, 2d singular present indicative ending — more at -est
— used to form the third person singular present of most verbs that do not end in s, z, sh, ch, or postconsonantal y
fall s
take s
play s
— compare -es II