To strike or assault someone violently and severely, typically on the head. He warned me that he was going to brain me if I didn't stop insulting him. The lump on my head is from when a box fell off a shelf and brained me yesterday.

Particularly stupid, foolish, or narrow-minded. The town hall meeting was hijacked by a few pea-brained morons trying to protest the new highway development. Don't let Tom's comments get you down—he's just a pea-brained jerk who puts other people down to make himself feel smart.

Describing someone who lacks intelligence or makes stupid decisions. You're so bird-brained. I can't believe you got stranded on the highway because you didn't put enough gas in your car!

Wacky or crazy. There's a guy on our corner who shouts about the end of the world; I think he's a little crackbrained. Oh please, that'll never work—it's a crackbrained idea.

Utterly foolish or poorly thought out. He's always got some lamebrained scheme to get rich.

rude slang Stupid or foolish. Oh, don't listen to any fuck-brained thing that guy has to say! It's freezing, and you came outside without a coat? Are you fuck-brained?