The word "un-becoming" is used to describe something that is inappropriate or unsuitable. Its antonyms would therefore be words that describe something that is suitable or appropriate. Some possible antonyms for "un-becoming" include becoming, appropriate, fitting, correct, proper, decent, suitable, and decorous, among others. These words all suggest that something is in line with the expected or desired standards, and is therefore seen as acceptable or desirable in a given context. Using these antonyms can help to convey a sense of positivity or approval, particularly in situations where un-becoming behavior or actions are being criticized or condemned.