WordNet (r) 3.0 (2006):

tail fin
    n 1: a stabilizer that is part of the vertical tail structure of
         an airplane [syn: vertical stabilizer, vertical
         stabiliser, vertical fin, tail fin, tailfin]
    2: one of a pair of decorations projecting above the rear
       fenders of an automobile [syn: tail fin, tailfin, fin]
    3: the tail of fishes and some other aquatic vertebrates [syn:
       tail fin, caudal fin]