The word "most spumescent" refers to something that is frothy, bubbly, or foamy. Its antonyms would indicate something that is not frothy or bubbly. The opposite of spumescent could be terms like flat, still, or calm. Other antonyms for spumescent could include words like clear, transparent, or pure, indicating the absence of froth or bubbles. Additionally, words like dense, solid, or heavy could be antonyms for spumescent, indicating something that has no air or gas trapped inside. Thus, the antonyms for the word "most spumescent" would vary based on the context and meaning of the sentence.