fin

(fĭn)

1. A membranous appendage extending from the body of a fish or other aquatic animal, used for propelling, steering, or balancing the body in the water.
2. Something resembling a fin in shape or function, as:
   a. A fixed or movable airfoil used to stabilize an aircraft, missile, or projectile in flight.
   b. A thin, usually curved projection attached to the rear bottom of a surfboard for stability.
   c. A projecting vane used for cooling, as on a radiator or an engine cylinder.
   d. See tail fin.
3. See flipper.

1. To emerge with the fins above water.
2. To swim, as a fish.
3. To lash the water with the fins. Used of a dying whale.

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fin¹

fins of a typical bony fish

(fĭn)