The Collaborative International Dictionary of English v.0.48:

fishtail \fishtail\ v. i.
   to have the rear end skid from side to side, out of control:
   -- said of automobiles or other vehicles.
   [PJC]

   Fish-tail burner, a gas burner that gives a spreading flame
      shaped somewhat like the tail of a fish.

   Fish-tail propeller (Steamship), a propeller with a single
      blade that oscillates like the tail of a fish when
      swimming.
      [1913 Webster]