What is the meaning of S'?

negates the meaning of the modified verb: not, don't

Apocopic form of se before a vowel

Contraction of es.

Elision of si (“if”) before il or ils.

Elision of se before a word beginning with a vowel.

Elision of se before a word beginning with a consonant.

Present/future copula form

Used to introduce the comparative/superlative form of adjectives

third-person singular reflexive pronoun; oneself

his; her; its (elided form of son or sa before a word starting with a vowel)

Apocopic form of se (“if”)

Apocopic form of si, used before a vowel

Apocopic form of su, used before a vowel: the (masculine singular definite article)

Apocopic form of sa, used before a vowel: the (feminine singular definite article)

Source: wiktionary.org

See also