tailrace

from WordNet (r) 3.0 (2006)

tailrace
    n 1: a watercourse that carries water away from a mill or water
         wheel or turbine

from The Collaborative International Dictionary of English v.0.48

Tailrace \Tail"race`\, n.
   1. See {Race}, n., 6.
      [1913 Webster]

   2. (Mining) The channel in which tailings, suspended in
      water, are conducted away.
      [1913 Webster]