The Collaborative International Dictionary of English v.0.48:

dehumidify \de*hu*mid"i*fy\ v. t.
   to remove the moisture from (air or another gas); to reduce
   the humidity of; as, The air conditioner dehumidifies the air
   in the summer.

   Syn: make less humid.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

dehumidify
    v 1: make less humid; "The air conditioner dehumidifies the air
         in the summer" [ant: humidify, moisturise,
         moisturize]