trade wind

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

• noun Any of a consistent system of prevailing winds occupying most of the tropics, constituting the major component of the general circulation of the atmosphere, and blowing northeasterly in the Northern Hemisphere and southeasterly in the Southern Hemisphere.

from The Century Dictionary.

• noun A wind that blows in a regular trade or course—that is, continually in the same direction.

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

• noun A steady wind that blows from east to west above and below the equator.

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

• noun steady winds blowing from east to west above and below the equator