The Collaborative International Dictionary of English v.0.48:

Feudalism \Feu"dal*ism\ (f[=u]"dal*[i^]z'm), n. [Cf. F.
   f['e]odalisme.]
   The feudal system; a system by which the holding of estates
   in land is made dependent upon an obligation to render
   military service to the king or feudal superior; feudal
   principles and usages.
   [1913 Webster]

WordNet (r) 3.0 (2006):

feudalism
    n 1: the social system that developed in Europe in the 8th
         century; vassals were protected by lords who they had to
         serve in war [syn: feudalism, feudal system]