- Brain-dead blends brain and dead. Medically speaking, it refers to human beings real state of being dead, not death of heart, nor death of lungs, but death of brain. Gradually people use brain-dead to describe someone's abnormal behaviors, just like someone makes such stupid and clumsy acts for his or her brain is not working thus controlling the body. It is a derogatory term, usually used in the situation that the speaker is really angry about someone's stupidity.
brain-dead
blending semantic change; adjective
Behaving as if having a malfunctioned brain. Usually describing dumb, clumsy, etc. behaviors.
Etymology : Blending of brain and dead, with semantic change from pure medically to a mundane derogatory term
Source : "What are you, brain-dead?" animation RWBY 2013.10
Last modified: 25 November 2013