late 15c., "degrading to a human,"from un- (1) "not" + manly (adj.). Similar formation in Middle Dutch onmamlijc, German unmännlich. Meaning "not having the qualities or attributes of a man" (as opposed to a woman or child) is from 1540s. Old English had unmennisclic "inhuman" (adj.); unmann (n.) "monster; wicked man."