- Severest class of psychological disorders, characterized by one or more of severe affective disturbances, profound introspection, withdrawal from reality, hallucinations, or regression.
Definition from: CRISP Thesaurus via Unified Medical Language System at the National Library of Medicine
- A serious mental disorder (as schizophrenia) characterized by defective or lost contact with reality often with hallucinations or delusions.
Definition from: Merriam-Webster's Medical Dictionary by Merriam-Webster Inc.
See also Understanding Medical Terminology.