1. a neurodevelopmental disorder characterized by markedly impaired social interactions and verbal and nonverbal communication; narrow interests; and repetitive behavior. Manifestations and features of the disorder appear before age 3 but vary greatly across children according to developmental level, language skills, and chronological age. They may include a lack of awareness of the feelings of others, impaired ability to imitate, absence of social play, abnormal speech, abnormal nonverbal communication, and a preference for maintaining environmental sameness. Classified in DSM–IV–TR as a pervasive developmental disorder, autism has been subsumed into autism spectrum disorder in DSM–5 and is no longer considered a distinct diagnosis. Also called autistic disorder; childhood autism; early infantile autism; infantile autism; Kanner’s syndrome.

2. in schizophrenia, an abnormal preoccupation with the self and fantasy such that there is a lack of interest in or ability to focus on external reality. —autistic adj.