noun

• (ichthyology, zootomy) One of the appendages of a fish, used to propel itself and to manoeuvre/maneuver.
  "The fish's fins minimize water flow."
• (surfing) A similar structure on the bottom of a surfboard, used to help steer it.
• (nautical) The conning tower of a submarine.
• (UK, slang, obsolete) A person's hand.
  ""Done say I to that, Reuben, tip me your fin, my spark, and it shall be a bet.""

verb

• (transitive) To cut the fins from a fish, shark, etc.
• (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."
• (intransitive) To swim in the manner of a fish.
  "A neutrally buoyant diver does not need to fin to maintain depth."
• (transitive) To provide (a motor vehicle etc) with fins.

noun

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

noun

• (archaic, film, television) "The end".
• (obsolete, road signs) Denotes the end of the road.