(now offensive) intellectually disabled, medically defined as having an IQ (intelligence quotient) below 70 in addition to deficits in two or more adaptive behaviors (which means having problems with basic functional skills that affect everyday, general living).

(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.

plural of mental hospital

Having a psychological disorder.

plural of mental gymnast

Someone who excels at mental gymnastics; a person who thinks creatively and effortlessly. / (derogatory) One who uses complex arguments to justify what is otherwise unjustifiable.

plural of mental reservation

The act of holding back some word or clause which is necessary to convey fully the meaning really intended by the speaker, distinct from equivocation.