cooling tower

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A large tower or similar structure typically attached to a power plant through which water is circulated to lower its temperature by partial evaporation.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A large device, in the form of a tower-shaped building, in which warm water is cooled by evaporation caused by circulating currents of air

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a cooling system used in industry to cool hot water (by partial evaporation) before reusing it as a coolant