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Related to brain dead: coma
1. Literally, lacking brain activity, as after a brain injury. After the car accident, Kendra was brain dead. Despite the surgeon's best efforts, the patient was brain dead.
2. slang So mentally exhausted or lacking focus that one does something poorly and/or makes easily avoidable mistakes. Did I just say that two plus two equals five? Wow, I'm really brain dead today.
mod. stupid. I don’t know why he’s so dull. He’s seems brain-dead half the time.