The Collaborative International Dictionary of English v.0.48:

Unbe \Un*be"\ ([u^]n*b[=e]"), v. t. [1st pref. un- + be.]
   To cause not to be; to cause to be another. [Obs. & R.]
   [1913 Webster]

         How oft, with danger of the field beset,
         Or with home mutinies, would he unbe
         Himself!                                 --Old Play.
   [1913 Webster]