I. (ˈ)mi|shüzə(r), (ˈ)mis|yüz- noun
Etymology: misuse (I) + -er
: one that misuses
these wretched misusers of language — S.T.Coleridge
II. noun
Etymology: Anglo-French, from Old French mesuser to misuse
: an unlawful use of a right ; especially : an unlawful use of a public office or grant of authority