fin

Etymology 1

From Middle English fin, from Old English finn, from Proto-Germanic *finnō, *finǭ (“dorsal fin”) (compare Dutch vin, German Finne, Swedish finne, fena), from Proto-Indo-European *(s)pīn- (“backbone, dorsal fin”) (compare Old Irish ind (“end, point”), Latin pinna (“feather, wing”), Tocharian A spin (“hook”), Sanskrit स्फ्य (sphyá, “splinter, staff”).

noun

1. (ichthyology) One of the appendages of a fish, used to propel itself and to manoeuvre/maneuver.
   The fish's fins minimize water flow.
   Then he commenced to talk, really talk. and inside of two flaps of a herring's fin he had me mesmerized, like Eben Holt's boy at the town hall show. He talked about the ills of humanity, and the glories of health and Nature and service and land knows what all. 1913, Joseph C. Lincoln, chapter 4, in Mr. Pratt's Patients
2. A similar appendage of a cetacean or other marine animal.
   a dolphin's fin
3. A thin, rigid component of an aircraft, extending from the fuselage and used to stabilise and steer the aircraft.
   The fin stabilises the plane in flight.
4. A similar structure on the tail of a bomb, used to help keep it on course.
5. A hairstyle, resembling the fin of a fish, in which the hair is combed and set into a vertical ridge along the top of the head from about the crown to the forehead.
6. A device worn by divers and swimmers on their feet.
   The divers wore fins to swim faster.
7. An extending part on a surface of a radiator, engine, heatsink, etc., used to facilitate cooling.
8. A sharp raised edge (generally in concrete) capable of damaging a roof membrane or vapor retarder.
9. (nautical) The conning tower of a submarine.

verb

1. (transitive) To cut the fins from a fish, shark, etc.
2. (intransitive) (Of a fish) to swim with the dorsal fin above the surface of the water.
   When you spot him finning just under the surface, you move up quietly and present … bait, usually a squid. 1983, The Fisherman Who Laughed, page 54
3. (intransitive) To swim in the manner of a fish.
   A neutrally buoyant diver does not need to fin to maintain depth.
4. (transitive) To provide (a motor vehicle etc) with fins.

Etymology 2

From Yiddish פֿינף (finf, “five”). Doublet of five, pimp, and finnuf.

noun

1. (UK, formerly Australia, slang) a five-pound (£5) note; the sum of five pounds.
2. (US, slang, dated) a five-dollar bill; the sum of five dollars.

Etymology 3

From French fin (“end”).

noun

1. (film, television, road signs) The finish, the end