Side-splitting is a term used to describe something that is extremely funny or hilarious. The antonyms for this word are words that describe the opposite of it, which means they describe something that is serious, dull, or not funny. Some antonyms for side-splitting are humorless, boring, drab, unamusing, unexciting, depressing, and tedious. These words are often used to classify things like movies, books, or jokes that do not elicit laughter or amusement. Although humor is subjective, the antonyms for side-splitting describe things that are generally agreed upon as not being funny or rather not enjoyable.