The Collaborative International Dictionary of English v.0.48:

Unbowel \Un*bow"el\, v. t. [imp. & p. p. Unboweledor
   Unbowelled; p. pr. & vb. n. Unboweling or Unbowelling.]
   [1st pref. un- + bowel.]
   To deprive of the entrails; to disembowel. --Dr. H. More.
   [1913 Webster]