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1.
wanting someone purely for their mind - has nothing to do with sexual attraction.
"i have such a brain crush on this kid in my philoshophy class. sure hes 5'3" and clearly never combs his hair, but he is so witty and articulate."
by woundedgazelle December 12, 2005
 
2.
When you have a crush on a person's brain, with complete disregard to appearance, availability, etc.
Laura has a braincrush on Thomas Jefferson.
by awesomeaardvark October 21, 2009