fin / fin/ • n. a flattened appendage on various parts of the body of many aquatic vertebrates and some invertebrates, including fish and cetaceans, used for propelling, steering, and balancing. ∎  a flipper for underwater swimming. ∎  a small flattened projecting surface or attachment on an aircraft, rocket, or automobile, providing aerodynamic stability or serving as a design element. ∎  a flattened projection on a device, such as a radiator, used for increasing heat transfer.DERIVATIVES: finned adj. [in comb.] primitive ray-finned fishes. ORIGIN: Old English finn, fin, of Germanic origin; related to Dutch vin and probably ultimately to Latin pinna ‘feather, wing.’

fin An appendage of fish and fish-like aquatic animals used for locomotion, steering, and balancing of the body. The skin fold forming the fin membrane is supported by cartilaginous, horny, or bony fin rays, which can be soft and flexible (soft rays) or hard and inflexible (fin spines). The median unpaired fins of fish include the dorsal fin on the back, the caudal fin (tail fin), and the anal fin behind the vent (anus). Usually there are also two pairs of lateral fins: the pectoral fins and the pelvic (also called ventral or abdominal) fins. See also APPENDICULAR SKELETON.

fins The locomotory organs of aquatic vertebrates. In fish there are typically one or more dorsal and ventral fins (sometimes continuous), whose function is balance; a caudal fin around the tail, which is the main propulsive organ; and two paired fins: the pectoral fins attached to the pectoral (shoulder) girdle and the pelvic fins attached to the pelvic (hip) girdle, which are used in steering. These paired fins are homologous with the limbs of tetrapods. Fins are strengthened by a number of flexible fin rays, which may be cartilaginous, bony and jointed, horny, or fibrous and jointed.

fin Appendage of fish and fish-like aquatic animals used for locomotion, steering, and balancing of the body. The skin fold forming the fin membrane is supported by cartilaginous, horny, or bony fin rays, which can be soft and flexible (soft rays) or hard and inflexible (fin spines).

fin OE. fin(n) = MLG. finne, MDu. vinne (Du. vin); prob. ult. rel. to L. pinna feather, wing.