Pronunciation enPR: fĭn, IPA (key): /fɪn/ Audio (US)(file) Noun Singular fin Plural fins The Simple English Wikipedia has an article on: Fin (countable) A fin is a wing like organ that is attached to some parts of the body of undersea animals. It is used for turning in a certain direction, balancing, and for propelling themselves. Some fish have a dorsal fin.Wikiwand - on Seamless Wikipedia browsing. On steroids.Remove ads