mid-14c., from Old French sauce, sausse, from Latin salsa "things salted, salt food," noun use of fem. singular or neuter plural of adjective salsus "salted," from past participle of Old Latin sallere "to salt," from sal (genitive salis) "salt" (see salt (n.)).
Meaning "something which adds piquancy to words or actions" is recorded from c.1500; sense of "impertinence" first recorded 1835 (see saucy, and cf. sass). Slang meaning "liquor" first attested 1940.