The Collaborative International Dictionary of English v.0.48:

Undispensable \Un`dis*pen"sa*ble\, a.
   1. Indispensable.
      [1913 Webster]

   2. Unavoidable; inevitable. [Obs.] --Fuller.
      [1913 Webster]

   3. Not to be freed by dispensation. [Obs.]
      [1913 Webster]