From non- + user.

nonuser (plural nonusers)

1. A person who is not a user (of drugs, a computer system, etc.).
2. (legal) Neglect or omission to use an easement or franchise or to assert a right.
   • 1765–1769, William Blackstone, Commentaries on the Laws of England, (please specify |book=I to IV), Oxford, Oxfordshire: […] Clarendon Press, →OCLC ↗:

     An office may be forfeited by mis-user or non-user.

   • 1826, James Kent, Commentaries on American Law:

     The subject of the forfeiture of corporate franchises by nonuser or misuser , was fully discussed in the case of The King v . Amery