Smooth
Old English smōth, probably of Germanic origin, though no cognates are known. The verb dates from Middle English.
wiktionary
From Middle English smoothe, smothe, smethe, from Old English smōþ and Old English smēþe, both from Proto-Germanic *smanþaz, *smanþiz, of unknown origin. Cognate with Scots smuith(“smooth”), Low German smood and smödig(“smooth, malleable, ductile”), Dutch smeuïg(“smooth”) (from earlier smeudig).
etymonline
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.
smooth (v.)
late Old English smoþ "to make smooth," replacing smeðan "to smooth, soften, polish; appease, soothe;" smeðian "smoothen, become smooth," from the source of smooth (adj.). Meaning "to make smooth" is c. 1200. Related: Smoothed; smoothing. Middle English also had a verb form smoothen (mid-14c.).
