Definition from macmillandictionary.com
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The human brain is divided into two halves.
The illness had affected his brain.
a brain tumour/scan/operation
She felt that she could almost see his brain working.
You have to use your brains in this job.
He’s good-looking, and he’s got brains.
The best brains in the country have failed to solve this problem.
It's James, he has a brain the size of a planet!