The Collaborative International Dictionary of English v.0.48:

Nonuser \Non*us"er\,
   1. A not using; failure to use.
      [1913 Webster]

            An office may be forfeited by misuser or nonuser.
                                                  --Blackstone.
      [1913 Webster]

   2. (Law) Neglect or omission to use an easement or franchise
      or to assert a right. --Kent.
      [1913 Webster]