Smug
mid 16th century (originally in the sense ‘neat, spruce’): from Low German smuk ‘pretty’.
wiktionary
Possibly from Middle Low German smuk(“lithe, delicate, neat, trim”) although the g of the English word is not easily explained. From the Low German derived also North Frisian smok, Danish smuk and Swedish smukk (now obsolete or dialectal). The ultimate source should be Proto-Germanic *smeuganą.
Compare Middle High German gesmuc(“ornament”) and smücken(“to dress, to adorn”), both ultimately from smiegen(“to press to, insert, wrap, to nestle”), hence German schmiegen, Schmuck and schmücken. The adjective schmuck, however, was borrowed from Low German. See smock for more.
etymonline
smug (adj.)
1550s, "trim, neat, spruce, smart," possibly an alteration of Low German smuk "trim, neat," from Middle Low German smücken "to adorn" (originally "to dress," secondary sense of words meaning "to creep or slip into"), from the same source as smock. The meaning "having a self-satisfied air" is from 1701, an extension of the sense of "smooth, sleek" (1580s), which was commonly used of attractive women and girls. Related: Smugly; smugness.
