The Collaborative International Dictionary of English v.0.48:

Fantail \Fan"tail`\ (f[a^]n"t[=a]l`), n. (Zool.)
   (a) A variety of the domestic pigeon, so called from the
       shape of the tail.
   (b) Any bird of the Australian genus Rhipidura, in which
       the tail is spread in the form of a fan during flight.
       They belong to the family of flycatchers.
   (c) the fantail goldfish.
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

fantail goldfish \fan"tail` gold"fish\, n. (Zool.)
   a type of goldfish bred artificially, having a realtively
   short oval body and a tail with four lobes arrayed somewhat
   like a folding fan, as though forming a part of the surface
   of a cone. Called also fantail.
   [PJC]

WordNet (r) 3.0 (2006):

fantail
    n 1: an overhang consisting of the fan-shaped part of the deck
         extending aft of the sternpost of a ship

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "fantail":
   brush, cauda, caudal appendage, caudation, counter, cue, dock,
   heel, pigtail, poop, queue, rattail, rudderpost, stern, stub, tail,
   tail end, tailpiece