The Collaborative International Dictionary of English v.0.48:

Rat-tail \Rat"-tail`\ (r[a^]t"t[=a]l`), a.
   Like a rat's tail in form; as, a rat-tail file, which is
   round, slender, and tapering. See Illust. of File.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rat-tail \Rat"-tail`\, n.
   1. (Far.) pl. An excrescence growing from the pastern to the
      middle of the shank of a horse.
      [1913 Webster]

   2. (Zool.)
      (a) The California chimaera. See Chimaera.
      (b) Any fish of the genus Macrurus. See Grenadier, 2.
          [1913 Webster]

WordNet (r) 3.0 (2006):

rattail
    n 1: deep-sea fish with a large head and body and long tapering
         tail [syn: grenadier, rattail, rattail fish]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "rattail":
   braid, brush, bun, cauda, caudal appendage, caudation, chignon,
   coil, cue, dock, fantail, knot, pigtail, plait, queue, stub, tail,
   tailpiece, topknot, twist