The Collaborative International Dictionary of English v.0.48:

Massacre \Mas"sa*cre\, v. t. [imp. & p. p. Massacred; p. pr. &
   vb. n. Massacring.] [Cf. F. massacrer. See Massacre, n.]
   To kill in considerable numbers where much resistance can not
   be made; to kill with indiscriminate violence, without
   necessity, and contrary to the usages of nations; to butcher;
   to slaughter; -- limited to the killing of human beings.
   [1913 Webster]

         If James should be pleased to massacre them all, as
         Maximian had massacred the Theban legion. --Macaulay.
   [1913 Webster]