The Collaborative International Dictionary of English v.0.48:

Probabilism \Prob"a*bil*ism\, n. [Cf. F. probabilisme.]
   The doctrine of the probabilists.
   [1913 Webster]

WordNet (r) 3.0 (2006):

probabilism
    n 1: a Roman Catholic system of casuistry that when expert
         opinions differ an actor can follow any solidly probable
         opinion that he wishes even though some different opinion
         might be more probable
    2: (philosophy) the doctrine that (since certainty is
       unattainable) probability is a sufficient basis for belief
       and action