psycho

Short definition from Wiktionary

Adjective

1. 1
   Psychotic, psychopathic, or (broadly) otherwise insane.

Noun

1. 1
   A person who is psychotic, psychopathic, or (broadly) otherwise insane.
2. 2
   A person who acts in a bizarre or dangerous manner.
3. 3
   A class, at a college or university, in which psychology is taught.