Dictionary.com
definitions

misuser

1
[mis-yoo-zer]
noun Law.
  1. abuse of a right; unlawful use of an office, franchise, benefit, etc.

Origin of misuser

1
1615–25; noun use of Middle French mesuser to misuse

misuser

2
[mis-yoo-zer]
noun
  1. a person who misuses.

Origin of misuser

2
First recorded in 1540–50; mis-1 + user1
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for misuser

misuser

noun
  1. law an abuse of some right, privilege, office, etc, such as one that may lead to its forfeiture
  2. (often in combination) a person who regularly abuses alcohol, drugs, etcheroin misusers

Word Origin for misuser

C17: from Old French mesuser (infinitive used as noun)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012