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]