The word "un-sightliest" means something that is not pleasant to look at. Antonyms for this word would be beautiful, attractive, charming, delightful, gorgeous, lovely, pleasing, and stunning. These words describe something that is visually pleasing and pleasant to look at. You can use these antonyms to describe anything from nature to art to people. For instance, a beautiful sunset, an attractive painting, a charming garden, a delightful perfume, a gorgeous dress, a lovely person, a pleasing melody, and a stunning landscape are all examples of things that are the opposite of un-sightliest. Using these antonyms will add color and variety to your descriptions and help make your writing more interesting and engaging.