Source : Webster's Revised Unabridged Dictionary (1913)

Decapitation \De*cap`i*ta"tion\, n. [LL. decapitatio: cf. F.
   d['e]capitation.]
   The act of beheading; beheading.

Source : WordNet®

decapitation
     n 1: execution by cutting off the victim's head [syn: {beheading}]
     2: killing by cutting off the head [syn: {beheading}]