1
- a person who is mentally ill (not in technical use)精神病患者, 疯子（非技术用语）。
1.1
- an extremely foolish or eccentric person极端愚蠢的人; 狂人：
this lunatic just accelerated out from the side of the road.
这个蠢货就从路边加速冲了出来。
attrib.
1- mentally ill (not in technical use)有精神病的（非技术用语）。
1.1
- extremely foolish, eccentric, or absurd极端愚蠢的;极端古怪的;极端荒谬的：
he would be asked to acquiesce in some lunatic scheme.
他会被要求默许某个极端荒唐的计划。
词源
Middle English: from Old French lunatique, from late Latin lunaticus, from Latin luna 'moon'(from the belief that changes of the moon caused intermittent insanity).