Smug is the look on someone who was right and wants you to see it. The colleague who backed up their files the day before the crash, sitting there with a small closed smile.
Smug goes with faces, smiles, tones and whole people: a smug grin, a smug little laugh, insufferably smug. It is always an insult — nobody describes themselves as smug. Being pleased with yourself is private and fine; being smug is being pleased where other people have to watch. The noun is smugness and the adverb is smugly, which is how the line gets delivered. Self-satisfied is the near neighbour, and complacent is close but adds the sense of doing nothing about a danger.
1adjectivesmugToo pleased with yourself, in a way that annoys other people.
“He gave a smug little nod when the numbers came in.”
synonyms: self-satisfied, complacent
Also accepted in games: self-satisfied
Smug started out meaning neat and well turned-out, borrowed from Low German smuk, 'pretty', and Middle Low German smuk, 'lithe, delicate, trim'. Further back sits a Germanic verb meaning to creep or press close, the family that also gave English smock. Somewhere on the way, looking pleased with yourself stopped counting as a compliment.
Proto-West Germanic
*smeugan — to crawl, creep
Middle Low German
smuk — lithe, delicate, neat, trim
Low German
smuk — pretty
English, today
smug
Originally "spruce, neat," from Low German smuk (“pretty”), from Middle Low German smuk (“lithe, delicate, neat, trim”), although the g of the English word is not easily explained. The ultimate source should be Proto-West Germanic smeugan (“to crawl, creep”). From the Low German - derived also frr smok, Danish smuk and Swedish smukk (now obsolete or dialectal). Compare also 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.
Etymology from Wiktionary, CC BY-SA