Source : Webster's Revised Unabridged Dictionary (1913)

Fin \Fin\, n.[OE. finne, fin, AS. finn; akin to D. vin, G. &
   Dan. finne, Sw. fena, L. pinna, penna, a wing, feather. Cf.
   {pen} a feather.]
   1. (Zo["o]l.) An organ of a fish, consisting of a membrane
      supported by rays, or little bony or cartilaginous
      ossicles, and serving to balance and propel it in the
      water.

   Note: Fishes move through the water chiefly by means of the
         caudal fin or tail, the principal office of the other
         fins being to balance or direct the body, though they
         are also, to a certain extent, employed in producing
         motion.

   2. (Zo["o]l.) A membranous, finlike, swimming organ, as in
      pteropod and heteropod mollusks.

   3. A finlike organ or attachment; a part of an object or
      product which protrudes like a fin, as:
      (a) The hand. [Slang]
      (b) (Com.) A blade of whalebone. [Eng.] --McElrath.
      (c) (Mech.) A mark or ridge left on a casting at the
          junction of the parts of a mold.
      (d) (Mech.) The thin sheet of metal squeezed out between
          the collars of the rolls in the process of rolling.
          --Raymond.
      (e) (Mech.) A feather; a spline.

   4. A finlike appendage, as to submarine boats.

   {Apidose fin}. (Zo["o]l.) See under {Adipose}, a.

   {Fin ray} (Anat.), one of the hornlike, cartilaginous, or
      bony, dermal rods which form the skeleton of the fins of
      fishes.

   {Fin whale} (Zo["o]l.), a finback.

   {Paired fins} (Zo["o]l.), the pectoral and ventral fins,
      corresponding to the fore and hind legs of the higher
      animals.

   {Unpaired, or Median}, {fins} (Zo["o]l.), the dorsal, caudal,
      and anal fins.