have something on the brain Definition

brain
noun

1. The highly developed mass of nervous tissue that co-ordinates and controls the activities of the central nervous system of animals.
2. colloq
Cleverness; intelligence.
Example: It takes brains to do that job
Thesaurus: intelligence, intellect, mind, gray matter, wits, faculties, common sense, mother wit.
Form: brains (especially)
3. colloq
A very clever person.
Thesaurus: genius, scholar, intellectual, egghead (slang), sage, savant, pundit, polymath.
Form: brains (especially)
Form: the brains
4. colloq
A person who thinks up and controls a plan, etc.
Example: He was the brains behind the idea
Form: brains (usually)

verb brained, braining

colloq:
1. To hit someone hard on the head.
2. To dash out or smash someone's brains.

Derivative: brained
adj

Note: especially in compounds
Having a brain or brains of a specified type.
Example: hare-brained
Example: scatterbrained

Derivative: brainless
adj

Lacking intelligence or sense
Thesaurus: stupid, dumb, daft, thoughtless, witless, empty-headed, idiotic, half-witted.

Derivative: brainlessly
adverb

Idiom: have something on the brain

colloq
To be unable to stop thinking about it; to be obsessed by it.

Idiom: pick someone's brains

See under pick.

Etymology: Anglo-Saxon brægen.