The Collaborative International Dictionary of English v.0.48:

Mercenary \Mer"ce*na*ry\, a. [OE. mercenarie, F. mercenaire, fr.
   L. mercenarius, fr. merces wages, reward. See Mercy.]
   1. Acting for reward; serving for pay; paid; hired; hireling;
      venal; as, mercenary soldiers.
      [1913 Webster]

   2. Hence: Moved primarily by considerations of pay or profit;
      greedy of gain; sordid; selfish. --Shak.
      [1913 Webster]

            For God forbid I should my papers blot
            With mercenary lines, with servile pen. --Daniel.
      [1913 Webster]

   Syn: See Venal.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mercenary \Mer"ce*na*ry\, n.; pl. Mercenaries.
   One who is hired; a hireling; especially, a soldier hired
   into foreign service. --Milman.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mercenary
    adj 1: marked by materialism [syn: materialistic, mercenary,
           worldly-minded]
    2: serving for wages in a foreign army; "mercenary killers"
       [syn: mercenary(a), free-lance(a), freelance(a)]
    3: profit oriented; "a commercial book"; "preached a mercantile
       and militant patriotism"- John Buchan; "a mercenary
       enterprise"; "a moneymaking business" [syn: mercantile,
       mercenary, moneymaking(a)]
    n 1: a person hired to fight for another country than their own
         [syn: mercenary, soldier of fortune]

Moby Thesaurus II by Grady Ward, 1.0:

85 Moby Thesaurus words for "mercenary":
   a hog for, acquisitive, adventurer, all-devouring, assistant,
   avaricious, avid, bottomless, bought, bribable, chartered,
   condottiere, corrupt, corruptible, coveting, covetous, devouring,
   drudge, employed, employee, esurient, free lance, girl Friday,
   gluttonous, gobbling, grabby, grasping, greedy, grub, grubber, gun,
   gunman, hack, hired, hired gun, hired hand, hired killer,
   hired man, hireling, hoggish, insatiable, insatiate, leased, let,
   limitless, man Friday, miserly, money-hungry, money-mad, myrmidon,
   omnivorous, on the take, overgreedy, paid, pensioner, piggish,
   predatory, professional killer, purchasable, quenchless, rapacious,
   ravening, ravenous, rented, right-hand man, slakeless, slavey,
   soldier of fortune, sordid, subleased, sublet, swinish,
   unappeasable, unappeased, unethical, unprincipled, unquenchable,
   unsated, unsatisfied, unscrupulous, unslakeable, unslaked, venal,
   voracious, worker