Un-imposing is the opposite of imposing, which means to demand attention, impress or intimidate. Some antonyms for un-imposing could be grandiose, impressive, conspicuous, or awe-inspiring. Something that is grandiose demands attention and is very impressive; something conspicuous is easily noticeable or stands out, while awe-inspiring evokes feelings of admiration or respect. Other antonyms for un-imposing could be magnificent or grandeur since they both signify something grand or impressively large in size, scale, or style. In contrast, something un-imposing bears no special quality, significance or effect, and would generally be considered ordinary or mediocre.