From Longman Dictionary of Contemporary Englishfinfin /fɪn/ ●○○ noun [countable] 1 
HBFone of the thin body parts that a fish uses to swim2 TTApart of a plane that sticks up at the back and helps it to fly smoothly3 TTC (also tail fin) a thin piece of metal that sticks out from a car or bomb at the back4 a flipper
HBFone of the thin body parts that a fish uses to swim2 TTApart of a plane that sticks up at the back and helps it to fly smoothly3 TTC (also tail fin) a thin piece of metal that sticks out from a car or bomb at the back4 a flipperExamples from the Corpus
fin• The caudal fin is yellow-brown, and the dorsal spine and long snout are orange.• When stocking a pool with fish, take care to select healthy individuals with firm, meaty bodies and erect dorsal fins.• This is a deep blue fish with red shading on his fins.• Almost all the major fins possess spines and venom glands.• Picture a shallow pool with a glassy surface, and in the pool picture minnows fluttering their tail fins but otherwise stationary.• Cars are fatter and fewer, and imitate animals with their fins and wings.From Longman Business DictionaryFinFin (also fin)FINANCE written abbreviation for FINANCEOrigin fin Old English finn 