The antonyms for the word "most nectarious" could be bitter, sour, unpleasant, unpalatable, or tasteless. Nectar is a sweet substance produced by flowers, so these antonyms describe the opposite of its taste. Bitter refers to a sharp, unpleasant taste, while sour is a tart, acidic taste. Unpleasant and unpalatable describe something that is disagreeable or difficult to swallow. Something that is tasteless lacks any notable flavor. While these words may not be commonly used to describe nectar, they paint a picture of what the opposite of "most nectarious" might be like.