brain
Definition
The principal organ of the central nervous system in vertebrates, located within the skull, responsible for processing sensory information, coordinating bodily functions, and enabling cognition, emotion, and memory.
The mind as the seat of intelligence, thought, and consciousness.
Informal: A highly intelligent or clever person.
Slang: The most important or essential part of something, akin to the 'brains' behind an operation.
Examples
My brain ghosted me during the job interview, leaving me staring blankly like a malfunctioning robot.
He's the brain of the heist crew, plotting schemes while the rest just provide the muscle and bad tattoos.
If brains were WiFi, she'd still be searching for a signal in the stone age.
Her brain runs on pure caffeine, turning Monday mornings into accidental poetry slams.