n. & v.
n. 1 an organ on various parts of the body of many aquatic vertebrates and some invertebrates, including fish and cetaceans, for propelling, steering, and balancing (dorsal fin; anal fin). 2 a small projecting surface or attachment on an aircraft, rocket, or motor car for ensuring aerodynamic stability. 3 an underwater swimmer's flipper. 4 a sharp lateral projection on the share or coulter of a plough. 5 a finlike projection on any device, for improving heat transfer etc.
v. (finned, finning) 1 tr. provide with fins. 2 intr. swim under water. fin-back (or fin whale) a rorqual, Balaenoptera physalus. finless adj. finned adj. (also in comb.).
[ OE fin(n) ]