flippant (adj.)youdaoicibaDictYouDict[flippant 词源字典]
c. 1600, "talkative, nimble in talk;" 1670s, "displaying unbecoming levity," apparently an extended form of flip (v.). The ending is perhaps modeled on other adjectives in -ant or a relic of the Middle English present participle ending -inde. Shortened form flip is attested from 1847. Related: Flippantly.[flippant etymology, flippant origin, 英语词源]
saucy (adj.)youdaoicibaDictYouDict
c. 1500, "resembling sauce," later "impertinent, flippantly bold, cheeky" (1520s), from sauce (n.) + -y (2). The connecting notion is the figurative sense of "piquancy in words or actions." Compare sauce malapert "impertinence" (1520s), and slang phrase to have eaten sauce "be abusive" (1520s). Also compare salty in same senses.