From Longman Dictionary of Contemporary Englishmental hospitalˈmental ˌhospital noun [countable] old-fashioned MHMPa hospital where people with mental illnesses are treated SYN psychiatric hospital
Examples from the Corpus
mental hospital• Her parents committed her to a mental hospital in Massachusetts.• Brown died April 30 at the state mental hospital.• Rocky himself, currently in a Texas mental hospital, will be released to play at the launch party! 