Mental illness and Psychological disorder

Mental illness noun - Any disease of the mind; the psychological state of someone who has emotional or behavioral problems serious enough to require psychiatric intervention.

Psychological disorder and mental illness are semantically related In some cases you can use "Psychological disorder" instead a noun phrase "Mental illness".

Psychological disorder noun - (psychiatry) a psychological disorder of thought or emotion; a more neutral term than mental illness.

Mental illness and psychological disorder are semantically related in disorder topic. You can use "Mental illness" instead a noun phrase "Psychological disorder".