The Collaborative International Dictionary of English v.0.48:

Port \Port\, n. [F. porte, L. porta, akin to portus; cf. AS.
   porte, fr. L. porta. See Port a harbor, and cf. Porte.]
   1. A passageway; an opening or entrance to an inclosed place;
      a gate; a door; a portal. [Archaic]
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            Him I accuse
            The city ports by this hath entered.  --Shak.
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            Form their ivory port the cherubim
            Forth issuing.                        --Milton.
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   2. (Naut.) An opening in the side of a vessel; an embrasure
      through which cannon may be discharged; a porthole; also,
      the shutters which close such an opening.
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            Her ports being within sixteen inches of the water.
                                                  --Sir W.
                                                  Raleigh.
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   3. (Mach.) A passageway in a machine, through which a fluid,
      as steam, water, etc., may pass, as from a valve to the
      interior of the cylinder of a steam engine; an opening in
      a valve seat, or valve face.
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   Air port, Bridle port, etc. See under Air, Bridle,
      etc.

   Port bar (Naut.), a bar to secure the ports of a ship in a
      gale.

   Port lid (Naut.), a lid or hanging for closing the
      portholes of a vessel.

   Steam port, & Exhaust port (Steam Engine), the ports of
      the cylinder communicating with the valve or valves, for
      the entrance or exit of the steam, respectively.
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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.
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   2. Pertaining to steam, air, gas, etc., that is released from
      the cylinder of an engine after having preformed its work.
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   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.
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