英语词源字典 - 在线词源网站

insinuate (v.)[insinuate 词源字典]: 1520s, from Latin insinuatus, past participle of insinuare "to throw in, push in, make a way; creep in, intrude, bring in by windings and curvings, wind one's way into," from in- "in" (see in- (2)) + sinuare "to wind, bend, curve," from sinus "a curve, winding" (see sinus). Sense of "to introduce tortuously or indirectly" is from 1640s. Related: Insinuated; insinuating; insinuatingly.[insinuate etymology, insinuate origin, 英语词源]
smooth (adj.): Old English smoð "smooth, serene, calm," variant of smeðe "free from roughness, not harsh, polished; soft; suave; agreeable," of unknown origin and with no known cognates. Of words, looks, "pleasant, polite, sincere" late 14c., but later "flattering, insinuating" (mid-15c.). Slang meaning "superior, classy, clever" is attested from 1893. Sense of "stylish" is from 1922.

Smooth-bore in reference to guns is from 1812. smooth talk (v.) is recorded from 1950. A 1599 dictionary has smoothboots "a flatterer, a faire spoken man, a cunning tongued fellow." The usual Old English form was smeðe, and there is a dialectal smeeth found in places names, such as Smithfield, Smedley.