An antonym for "un imposing" is "imposing". An imposing person or thing is impressive, commanding, and authoritative, while an un imposing person or thing is unremarkable and lacks the ability to draw attention. Other antonyms for "un imposing" include imposing, noticeable, striking, commanding, bold, authoritative, impressive, and dominant. These are words that express power, strength, and dominance. It's important to understand antonyms because they help us understand the full range of meaning of words, and can help us communicate more effectively by choosing the best words to convey our thoughts and ideas.