Meaning of -'S in English

-'S

~ 1 [ s , z after a vowel sound or voiced consonant, ɪz after a sibilant]

■ suffix denoting possession in singular nouns, also in plural nouns not having a final -s : John's book.

Origin

OE, masculine and neut. genitive singular ending.

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~ 2 [ s , z after a vowel sound or voiced consonant, ɪz after a sibilant]

■ suffix denoting the plural of a letter or symbol: 9's.

Concise Oxford English vocab.      Сжатый оксфордский словарь английского языка.