The Collaborative International Dictionary of English v.0.48:

Humanitarianism \Hu*man`i*ta"ri*an*ism\, n.
   1. (Theol. & Ch. Hist.) The distinctive tenet of the
      humanitarians in denying the divinity of Christ; also, the
      whole system of doctrine based upon this view of Christ.
      [1913 Webster]

   2. (Philos.) The doctrine that man's obligations are limited
      to, and dependent alone upon, man and the human relations.
      [1913 Webster]

WordNet (r) 3.0 (2006):

humanitarianism
    n 1: the doctrine that people's duty is to promote human welfare
         [syn: humanitarianism, humanism]

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "humanitarianism":
   BOMFOG, Benthamism, Christian charity, Christian love, agape,
   altruism, beneficence, benevolence, benevolent disposition,
   benevolentness, bigheartedness, brotherly love, caritas,
   charitableness, charity, do-goodism, flower power, generosity,
   giving, goodwill, grace, greatheartedness, largeheartedness, love,
   love of mankind, philanthropism, philanthropy, utilitarianism,
   welfarism, well-disposedness