An erection caused by intense intellectual thought. Came to inception due to its rhyming with the word/phrase "hard-on".
Bill got a raging smart-on when he realized all of the work that goes into the creation of a single pencil.
by TronsauseFiveMillion December 06, 2010

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Top Definition
An engorged penis (or its metaphorical equivalent, a state of sexual or quasi-sexual arousal) that results from intellectual stimulation.
Baby, the way your tongue trips across the philosophical terminology and so cleverly articulates the existential quandary--you really give me a smart on.
by joelmw October 23, 2010

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See smart on.
It saddens me to think that the intellectually challenged are incapable of a smart-on. But a good, liberal arts education is the sure cure for their cerebral impotence.
by joelmw October 24, 2010

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See smart on.
I sat with my woman discussing life's imponderables and ended up with hardcore smarton.
by joelmw October 24, 2010

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When you suddenly think of something awesome. Like a hard-on but with your brain.
Mike- we need some new ideas
James- OH MY GOSH I just had a smart-on! What if we build a waterproof phone!
Mike- THAT'S GENIUS
by ImSoCoolLolJk January 01, 2013

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what a woman on crack says to you in macdonalds after asking if you're in a cult...
"hey, are you guys in a cult?"
"no"
"oh well...smart on!!!"
by whoopie Goldberg January 29, 2008

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