Compos mentis is a Latin phrase that means having full control of one's mind, being of sound mind or sanity. Antonyms for compos mentis include: insane, deranged, demented, irrational, delirious, psychotic, unsound, crazy or mad. These words are used to describe a state of mental instability or illness, which may cause a person to behave in an unpredictable and dangerous manner. It is important to acknowledge the seriousness of such conditions and seek professional help if you or someone you know is experiencing them. Maintaining good mental health is crucial for leading a happy and fulfilling life.