(usually clothing) Initialism of small (of the manufactured size).

The nineteenth letter of the English alphabet, called ess and written in the Latin script.

The ordinal number nineteenth, derived from this letter of the English alphabet, called ess and written in the Latin script.

(set theory) An axiomatic set theory, developed by logician George Boolos, in which several of the axioms of ZF are derivable as theorems.

(UK, dialect) Contraction of as (when it is (nonstandardly) used as a relative conjunction, or like a relative pronoun, meaning "that").

Contraction of us (found in the formula let’s which is used to form first-person plural imperatives).

Used in the formation of certain English adverbs.

(UK, dialect) Contraction of as.

(poetic) Contraction of his.

(metrology) Abbreviation of scruple. (unit of mass in the apothecaries' system) / (physics) Abbreviation of strange quark. / Alternative form of s.