The Collaborative International Dictionary of English v.0.48:

Psychosis \Psy*cho"sis\, n. [NL. See Psycho-.]
   [1913 Webster]
   1. Any vital action or activity. --Mivart.
      [1913 Webster]

   2. (Med.) A disease of the mind; especially, a functional
      mental disorder, that is, one unattended with evident
      organic changes.
      [1913 Webster]

WordNet (r) 3.0 (2006):

psychosis
    n 1: any severe mental disorder in which contact with reality is
         lost or highly distorted

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "psychosis":
   abulia, arteriosclerotic psychosis, brain disease, certifiability,
   crack-up, dementia paralytica, dipsomania, drug addiction,
   emotional disorder, emotional instability, folie du doute,
   functional nervous disorder, functional psychosis,
   general paralysis, general paresis, insanity, maladjustment,
   manic-depressive psychosis, melancholia, mental disorder,
   mental illness, metabolic psychosis, moral insanity,
   nervous breakdown, nervous disorder, neurosis, organic psychosis,
   paralytic dementia, paranoia, pathological drunkenness,
   personality disorder, presenile dementia, prison psychosis,
   problems in living, psychopathia, psychopathia sexualis,
   psychopathic condition, psychopathic personality, psychopathy,
   reaction, schizophrenia, senile dementia, senile psychosis,
   senility, sexual pathology, situational psychosis,
   social maladjustment, syphilitic paresis, toxic psychosis