One's emotional well-being, especially with reference to one's outlook on life, ability to cope with stress or the absence of a mental disorder.

(dated) mental hospital

plural of mental disorder

(psychiatry) A behavioral or mental pattern that may cause suffering or a poor ability to function in life.

plural of trench mentality

plural of mental midget

(informal) A stupid person.

plural of mental aberration

A deviation in mental function.

(UK, slang) An insane person; a nutcase.