(derogatory, vulgar slang) Extremely stupid.

(derogatory, vulgar slang) An extremely stupid person.

Surgery on any part of the nervous system, especially the brain; neurosurgery. / (uncountable, idiomatic) Something that is overly complex, detailed or confusing.

(figuratively, slang, mildly vulgar) Something ill-considered and said or done impulsively. / (figuratively, slang, mildly vulgar) An instance of absent-mindedness or forgetfulness.

(cytology) A cell in the brain, such as a neuron or a glial cell. / (colloquial) neuron / (humorous) -- taken as a unit of intelligence

Any of several species of coral with the appearance of a brain, in the families Mussidae and Merulinidae.

Any mass educational system of improving or providing conditions to increase the intellectual quality and yield of a population of (human) brains, e.g. a university or school.

Synonym of knowledge worker

(chiefly Britain) A group of experts who discuss events in public, especially on television or radio.

(chiefly US) Originally, a group of experts who advise a government, often informally. / More recently, any group of experts assembled to give advice.