The Collaborative International Dictionary of English v.0.48:

Altruism \Al"tru*ism\, n. [F. altruisme (a word of Comte's), It.
   altrui of or to others, fr. L. alter another.]
   Regard for others, both natural and moral; devotion to the
   interests of others; brotherly kindness; -- opposed to
   egoism or selfishness. [Recent] --J. S. Mill.
   [1913 Webster]

WordNet (r) 3.0 (2006):

altruism
    n 1: the quality of unselfish concern for the welfare of others
         [syn: altruism, selflessness] [ant: egocentrism,
         egoism, self-centeredness, self-concern, self-
         interest]