Fin, n.
 1. Zool. 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. Zool. 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.]   (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.
 (e) Mech. A feather; a spline.
 4. A finlike appendage, as to submarine boats.
 5. Aëronautics A fixed stabilizing surface, usually vertical, similar in purpose to a bilge keel on a ship.
 Apidose fin. Zool. 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 Zool., a finback.
 Paired fins Zool., the pectoral and ventral fins, corresponding to the fore and hind legs of the higher animals.
 Unpaired fins, or Median fins Zool., the dorsal, caudal, and anal fins.

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 fin whale
      n : large flat-headed whalebone whale having deep furrows along
          the throat; of Atlantic and Pacific [syn: finback, {finback
          whale, common rorqual, Balaenoptera physalus]