The Collaborative International Dictionary of English v.0.48:

Mutualism \Mu"tu*al*ism\, n. (Ethics)
   The doctrine of mutual dependence as the condition of
   individual and social welfare. --F. Harrison. --H. Spencer.
   --Mallock.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mutualism
    n 1: the relation between two different species of organisms
         that are interdependent; each gains benefits from the other
         [syn: symbiosis, mutualism]