loss leader

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

• noun A commodity offered especially by a retail store at cost or below cost to attract customers.

from the GNU version of the Collaborative International Dictionary of English.

• noun an article of merchandise sold at a loss in order to draw customers.

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

• noun marketing An item that is sold at or below cost in an effort to stimulate other profitable sales.

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

• noun a featured article of merchandise sold at a loss in order to draw customers