The Collaborative International Dictionary of English v.0.48:

Decapitate \De*cap"i*tate\, v. t. [imp. & p. p. Decapitated;
   p. pr. & vb. n. Decapitating.] [LL. decapitatus, p. p. of
   decapitare; L. de- + caput head. See Chief.]
   1. To cut off the head of; to behead.
      [1913 Webster]

   2. To remove summarily from office. [Colloq. U. S.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

decapitated \decapitated\ adj.
   having had the head cut off.

   Syn: beheaded.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

decapitated
    adj 1: having had the head cut off; "the beheaded prisoners"
           [syn: beheaded, decapitated]