psychosis /sīkō″sis/ pl. psychoses [Gk, psyche + osis, condition] , any major mental disorder of organic or emotional origin characterized by a gross impairment in reality testing, in which the individual incorrectly evaluates the accuracy of his or her perceptions and thoughts and makes incorrect references about external reality, even in the face of contrary evidence. It is often characterized by regressive behavior, inappropriate mood and affect, and diminished impulse control. Symptoms of psychoses include hallucinations and delusions. See also acute psychosis, ambulatory schizophrenia.
