1 having serious brain damage and needing a machine to stay alive 脑死亡的（指脑部严重受损，需要机器帮助才能存活）

2 (informal 非正式) unable to think clearly; stupid 不能清晰思考；呆头呆脑: He's brain-dead from watching too much TV. 他电视看得太多，变得呆头呆脑。