The Collaborative International Dictionary of English v.0.48:

decollate \de*col"late\ (d[-e]*k[o^]l"l[=a]t), v. t. [imp. & p.
   p. Decollated; p. pr. & vb. n. Decollating.] [L.
   decollatus, p. p. of decollare to behead; de- + collum neck.]
   To sever from the neck; to behead; to decapitate.
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         The decollated head of St. John the Baptist. --Burke.
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The Collaborative International Dictionary of English v.0.48:

Decollated \De*col"la*ted\, a. (Zool.)
   Decapitated; worn or cast off in the process of growth, as
   the apex of certain univalve shells.
   [1913 Webster]