The word "sidesplittingly" is used to describe something that is extremely funny or amusing. There are many synonyms that can be used to convey this same meaning, such as uproariously, hysterically, gut-bustingly, knee-slappingly, rib-ticklingly, and side-splittingly humorous. Other words that can be used to describe something that is funny or amusing include comical, humorous, witty, amusing, and entertaining. Whether you are looking for a casual way to say something is funny or want to describe something in a more formal context, there are many different words and phrases to choose from to express the idea that something is truly hilarious.