The Collaborative International Dictionary of English v.0.48:

Vitalism \Vi"tal*ism\, n. (Biol.)
   The doctrine that all the functions of a living organism are
   due to an unknown vital principle distinct from all chemical
   and physical forces.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vitalism
    n 1: (philosophy) a doctrine that life is a vital principle
         distinct from physics and chemistry