The word 'zaniest' is an adjective that means 'being or characteristic of a zany; clownish or ludicrously comical.' The antonyms for 'zaniest' may include the words 'serious,' 'sober,' 'grave,' 'solemn,' 'thoughtful,' 'calm,' 'composed,' 'judicious,' and 'reasonable.' These words refer to states of being that are opposite or opposite in character to the zaniness or comicality implied by the word 'zaniest.' Some other antonyms could be 'dull,' 'tedious,' 'dreary,' 'boring,' or 'humdrum,' which all refer to things that lack excitement, liveliness, or whimsy.