A patient at a mental illness institution.

plural of mental patient

(euphemistic) Having low intelligence. / (euphemistic) Having a mental illness.

A hospital facility designed to treat persons with serious mental disorders, as opposed to disorders of the body.

(slang) Engaging in intellectually stimulating conversation with little or no practical purpose. / (slang) Thought processes that only serve to satisfy oneself.

(idiomatic, Philippines) A way of thinking best described by the phrase "if I can't have it, neither can you." The metaphor refers to a pot of crabs in which one tries to escape over the side, but is relentlessly pulled down by the others in the pot.

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

(psychology, dated) A developmental disability in which the person has a very low intelligence quotient, usually below 70, plus difficulty in multiple areas of daily life. Evidence of this disability must have appeared before the person reached adulthood for diagnosis.

plural of mental breakdown

Difficult and complex logical thought processes, especially when performed effortlessly. / (derogatory) Inventive, complex arguments used to justify what is otherwise unjustifiable.