The term 'mentally deranged' is often used to describe someone who is suffering from a mental illness, such as psychosis. A PSYCHOTIC disorder is characterized by a loss of contact with reality, and can include symptoms such as delusions, hallucinations, disorganized thinking, and difficulty functioning in everyday life. The crossword solution for this term is 'PSYCHOTIC, ' which is a nine-letter word that describes someone who is experiencing a PSYCHOTIC disorder.