Source : WordNet®

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