Top Definition
Someone who is really smart but lacks wisdom.
He is a rare species of brain fish, floating around his bowl thinking about important theories but he'll never able to actually apply any of it.
by Peaceful_Idiot April 08, 2011
1 more definition
A large species of fish that explodes into millions of little brainfish in order to reproduce.

Also a term for a fish that thinks they know it all.
God, that guppy is such a brainfish!
by NovaMetatail July 07, 2009

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