'smartass' is an English compound formed from 'smart' + 'ass'. The compound emerged in American slang in the late 19th to early 20th century, combining 'smart' (meaning clever or sharp) with 'ass' used as a coarse term for a foolish or obnoxious person.

'smart' comes from Old English 'smeart' (originally meaning 'painful' or 'sharp') and evolved through Middle English to mean 'quick, clever' in modern use. 'Ass' as an insult is related to Old English forms (and also to Latin 'asinus' for the animal 'ass'), while 'arse' (Old English 'ærse') influenced coarse terms for buttocks and, by extension, for a stupid or contemptible person. The two words were joined colloquially to produce the insulting compound 'smartass'.

Initially a blunt compound describing someone both 'clever' and contemptible, over time it settled on the sense 'an annoyingly clever or sarcastic person' and is now primarily an informal/pejorative term.