Definition of lunatic adjective from the Oxford Advanced American Dictionary

lunatic

adjective
/ˈlunəˌtɪk/
 
 
crazy, ridiculous, or extremely stupidlunatic ideasa lunatic smileIDIOM

the lunatic fringe

(disapproving) those members of a political or other group whose views are considered to be very extreme and crazyThey stressed that only the lunatic fringe of the movement was involved in the incident.the lunatic fringe