Noun
A fin at the tail of a fish, caudal fin
A fin on the tail of an aircraft, vertical stabilizer
(automotive) A fin-like projection at the rear of a car, common on American cars of the 1950s.
Source: en.wiktionary.orgThe current United livery consists of a white upper fuselage, with a gold globe on a blue tailfin, and a gray underbelly. Source: Internet
Samlesbury (4000 employees) makes air-frames; the front fuselage, canards and tailfin of the Eurofighter. Source: Internet