The Collaborative International Dictionary of English v.0.48:

Unget \Un*get"\, v. t. [1st pref. un- + get.]
   To cause to be unbegotten or unborn, or as if unbegotten or
   unborn. [R.]
   [1913 Webster]

         I 'll disown you, I 'll disinherit you, I 'll unget
         you.                                     --Sheridan.
   [1913 Webster]