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.
Phrases and idioms:
fin-back (or fin whale) a rorqual, Balaenoptera physalus.
Derivatives:
finless adj. finned adj. (also in comb.).
Etymology: OE fin(n)