1. contraction of it is: It's starting to rain. 2. contraction of it has: It's been a long time.

s suff. Used to form the possessive case of singular nouns, plural nouns that do not end in s, certain pronouns, and phrases that function as nouns or pronouns: nation's; women ...

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... music theory and performance practice or music theory and ethnomusicology and the study of the reception and history of music, generally called musicology. Xenakis's definition

noun pl. S's, s's. the nineteenth letter of the English alphabet: from the Greek sigma, a borrowing from the Phoenician; any of the speech sounds that this letter represents, as ...