noun - the pseudo-brain you have in your anus, that you inadvertently use to make stupid decisions or make you say stupid things, as opposed to using your actual brain. (2)Name used to describe someone who used his/ass and therefore "brainus" to make a decision that was stupid.
That's using your brainus... idiot!
Nice work on that one brainus.
by Jonathan Ainslie August 13, 2006
Top Definition
The word to describe the combined body part created when one shoves their head up their ass.
He's got NO I.Q., he's a walking brainus.
by Phuqit November 12, 2006
One of three categorizations of an answer (other two: anus and brain--see definition); meaning you are not 100% certain that your answer is 100% true
"Lions can run 100 mph."
"Brain, Brainus, or Anus?"
"Ummmm, Brainus."
by spintas March 12, 2012
The region of the brain where ideas or thoughts of utter stupidity are formed.
Tom's decision to wear a leisure suit to his father-in-law's funeral clearly came out of his brainus.
by Antonym Antony January 30, 2011
The aperture through which the work of creative and talented people emerges.

So, Paul, what contributions to human endeavour have come out of your brainus this morning?

by Tiahlm September 10, 2007
The occurence of putting one person's testicle(s) inside another person's anus.
He gave her the brainus.
by Roddy von Seldeneck May 05, 2007
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