The Collaborative International Dictionary of English v.0.48:

Exhaust \Ex*haust"\, a. [L. exhaustus, p. p.]
   1. Drained; exhausted; having expended or lost its energy.
      [1913 Webster]

   2. Pertaining to steam, air, gas, etc., that is released from
      the cylinder of an engine after having preformed its work.
      [1913 Webster]

   Exhaust draught, a forced draught produced by drawing air
      through a place, as through a furnace, instead of blowing
      it through.

   Exhaust fan, a fan blower so arranged as to produce an
      exhaust draught, or to draw air or gas out of a place, as
      out of a room in ventilating it.

   Exhaust nozzle, Exhaust orifice (Steam Engine), the blast
      orifice or nozzle.

   Exhaust pipe (Steam Engine), the pipe that conveys exhaust
      steam from the cylinder to the atmosphere or to the
      condenser.

   Exhaust port (Steam Engine), the opening, in the cylinder
      or valve, by which the exhaust steam escapes.

   Exhaust purifier (Milling), a machine for sorting grains,
      or purifying middlings by an exhaust draught. --Knight.

   Exhaust steam (Steam Engine), steam which is allowed to
      escape from the cylinder after having been employed to
      produce motion of the piston.

   Exhaust valve (Steam Engine), a valve that lets exhaust
      steam escape out of a cylinder.
      [1913 Webster]

WordNet (r) 3.0 (2006):

exhaust fan
    n 1: a fan that moves air out of an enclosure