The word "most gelastic" refers to something that is highly funny or humorous. As for its antonyms, we can consider words like "unfunny", "unamusing", "serious", and "sober". These words indicate the opposite of being funny or humorous. If someone says a joke that doesn't make us laugh, we might describe it as "unfunny" or "unamusing". Similarly, when we talk about situations or topics that require a serious and somber attitude, we may use words like "serious" or "sober", indicating that there is no room for humor or laughter. Therefore, antonyms of "most gelastic" help us describe situations where humor is not appropriate or simply absent.