Source : Webster's Revised Unabridged Dictionary (1913)

Air pump \Air" pump`\
   1. (Physics) A kind of pump for exhausting air from a vessel
      or closed space; also, a pump to condense air or force it
      into a closed space.

   2. (Steam Engines) A pump used to exhaust from a condenser
      the condensed steam, the water used for condensing, and
      any commingled air.

Source : WordNet®

air pump
     n : a pump that moves air in or out of something [syn: {vacuum
         pump}]