Real Dictionary

fin
countable noun: A fin on something such as an aeroplane, rocket, or bomb is a flat part which sticks out and which is intended to help control its movement.
countable noun: A fish's fins are the flat objects which stick out of its body and help it to swim and keep its balance.

Fin in American English
Finland

fin in American English 1
any of several winglike, membranous organs on the body of a fish, dolphin, etc., used in swimming, turning, and balancing
to cut the fins from (a fish)
to move the fins, esp. in a violent way
noun: a membranous, winglike or paddlelike organ attached to any of various parts of the body of fishes and certain other aquatic animals, used for propulsion, steering, or balancing

fin in American English 2
noun: a five-dollar bill

fin in American English 3
the end; finish; conclusion

fin in American English 4
finance

Fin in British English
abbreviation for: Finland
abbreviation for: Finland (international car registration)

fin in British English 1
noun: any of the firm appendages that are the organs of locomotion and balance in fishes and some other aquatic animals. Most fishes have paired and unpaired fins, the former corresponding to the limbs of higher vertebrates

fin in British English 2
noun: a five-dollar bill

fin in Chemical Engineering
noun: A fin is a plate or other object which is attached to a surface in order to improve the flow of heat.

fin in Mechanical Engineering
noun: A fin is a plate or other object which is attached to a surface in order to improve the flow of heat.

fin. in American English
abbreviation: finance
abbreviation: Finland

fin. in British English
abbreviation for: finance