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 ]
v. t. to render (gases, especially air) humid or to increase the moisture content of; as, We have a machine that humidifies the air in the house. Syn. -- moisturize, make humid, make more humid. [ WordNet 1.5 ]