psy·cho I. \ˈsī(ˌ)kō\noun (-s) Etymology: by shortening 1.: psychoanalysis 2.[short for psychoneurotic]: one who has developed an emotional disorder (as a psychoneurosis) < most of your clients are pimps, drug dealers, and psychos > II. adjective Etymology: by shortening 1.: psychiatric < psycho ward > 2.: psychoneurotic < psycho cases > III. transitive verb (-ed/-ing/-s) slang: psychoanalyze