C2 mentally ill疯癫的,精神失常的
For the last ten years of his life he was clinically insane.在生命的最后10年,他处于临床上的精神失常状态。
informal I sometimes think I'm going insane (= I feel very confused).我有时觉得自己快要疯了。
C1 extremely unreasonable or stupid疯狂的;荒唐的
It would be insane not to take advantage of this opportunity.如果不抓住这一机会的话那就太荒唐了。