Unprepossessing is an adjective that describes something that is plain or unattractive in appearance or lacking charm or appeal. Antonyms for unprepossessing include words like attractive, charming, appealing, beautiful, and stunning. If something is unprepossessing, it's not likely to catch the eye or hold attention, but its opposite traits will do precisely that. People or things that are prepossessing have qualities that are pleasing or charming to others, and they often cause admiration or adoration. Alternatively, uninspiring, unexciting or dull can also capture the idea of unprepossessing.