mercenary

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

• adjective Motivated solely by a desire for monetary or material gain.
• adjective Hired for service in a foreign army.
• noun One who serves or works merely for monetary gain; a hireling.
• noun A professional soldier hired for service in a foreign army.

from The Century Dictionary.

• Working or acting for reward; hired; serving only for gain; selling one's services to the highest bidder.
• Hence Venal; sordid; actuated only by hope of reward; ready to accept dishonorable gain: as, a mercenary prince or judge; a mercenary disposition.
• Pertaining or due to hope of gain or reward; done, given, etc., in return for hire; resulting from sordid motives: as, mercenary services; a mercenary act.
• Synonyms Hireling, etc. See venal.
• noun A person who works for pay: especially, one who has no higher motive to work than love of gain.
• noun Specifically, a soldier in foreign service; a professional soldier.

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

• noun One who is hired; a hireling; especially, a soldier hired into foreign service.
• adjective Acting for reward; serving for pay; paid; hired; hireling; venal.
• adjective Moved primarily by considerations of pay or profit; greedy of gain; sordid; selfish.

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

• adjective Motivated by private gain.
• noun A person employed to fight in an armed conflict who is not a member of the state or military group for which they are fighting and whose prime or sole motivation is private gain.

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

• adjective serving for wages in a foreign army
• adjective profit oriented
• adjective marked by materialism
• noun a person hired to fight for another country than their own