Definition of: brain

(brān) noun
1. Anat. The enlarged and greatly modified portion of the central nervous system contained within the cranium of vertebrates: its functions are shared between the two cerebral hemispheres, the cerebellum, and the medulla oblongata, which are of great development in higher mammals and in man.
2. Mind; intellect: often in the plural.
3. Zool. The principal regulating ganglion of invertebrates. See synonyms under MIND.
—to have on the brain To be obsessed by.
—v.t. To dash out the brains of. [OE brœgen]