The word "zestier" refers to something that is full of energy, enthusiasm, and excitement. Antonyms of this word include dull, flat, and lifeless. Something without zest is lacking in spirit or liveliness, making it mundane and unexciting. Tepid, vapid, and insipid are other antonyms that can be used for zestless. If something lacks flavor, it is said to be bland, while if it is lacking in excitement, it would be considered boring. Hence, a person can use a number of antonyms to describe something that is opposite to zestier.