The Collaborative International Dictionary of English v.0.48:

Selflessness \Self"less*ness\, n.
   Quality or state of being selfless.
   [1913 Webster]

WordNet (r) 3.0 (2006):

selflessness
    n 1: the quality of unselfish concern for the welfare of others
         [syn: altruism, selflessness] [ant: egocentrism,
         egoism, self-centeredness, self-concern, self-
         interest]
    2: acting with less concern for yourself than for the success of
       the joint activity [syn: selflessness, self-sacrifice]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "selflessness":
   Olympian detachment, altruism, commitment, consecration,
   dedication, detachment, devotion, disinterest, disinterestedness,
   dispassion, dispassionateness, humility, impartiality, loftiness,
   modesty, neutrality, sacrifice, self-abasement, self-abnegation,
   self-denial, self-devotion, self-effacement, self-forgetfulness,
   self-immolation, self-neglect, self-neglectfulness,
   self-renouncement, self-sacrifice, self-subjection,
   unacquisitiveness, unbias, unbiasedness, unpossessiveness,
   unselfishness