idioms brain 1
a bird brain (a stupid person): I’m such a birdbrain. I forgot to tank up at the gas station.
a brain drain (a situation in which a large number of educated and highly skilled people leave their own country):
all brawn and no brains (physically strong but not very intelligent)
brain dead (very stupid or careless): These kind of criminals are also the most brain dead people in the country.
brain dead (mentally exhausted and unable to think normally)
be the brains behind (be the person who provides ideas and plans for an activity): He was in fact the brains behind the bank robbery.
beat your brains out (think very hard about how to deal with a problem): I’ve been beating my brains out all week trying to find a solution indeed.
beat someone’s brains out (hurt someone badly): If you come back again, I’ll beat your brains out.