-'s

[суффикс, вторая часть сложных слов] образует форму притяжательного падежа существительных Например: my sister's letter — письмо моей сестры Bill's purse — кошелёк Билла -'s

Большой англо-русский словарь

-'s

noun suffix or pronoun suffix Etymology: Middle English -es, -s, genitive singular ending, from Old English -es; akin to Old High German -es, genitive singular ending, Greek -oio, -ou, Sanskrit -asya — used to form the possessive of singular nouns Example: boy's, of plural nouns not ending in s Example: children's, of some pronouns Example: anyone's, and of word groups functioning as nouns Example: the man in the corner's hat or pronouns Example: someone else's

Merriam-Webster's Collegiate Dictionary