Meaning of -S in English

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

Merriam-Webster's Collegiate English vocabulary.      Энциклопедический словарь английского языка Merriam Webster.