To prepare to kick another's ass, getting prepared to engage in fisticuffs
If you get up in my grille, you best knuckle up, motherfucker
by stefanali pops September 13, 2005
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a phrase uttered in encouragement meaning: "muster your courage, intestinal fortitude and love for the American-way in preparation for an upcoming (or admist a) challenge
of epic proportions!"
(uttered many times by one of the dudes in the movie "The Matrixs:Revolutions" during battle
against the electro-mechanical foe)
"Here they come boys ... Knuckle up!"
by abc July 13, 2004
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To Make Reddy, To Make Preparation, To Assemble, To Focus on the objective, To concentrate
Tomorrow's the big day people, there's no room for mistakes, so all of you better Knuckle-Up!
by ElkarO November 05, 2003
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major shrinkage of a man's penis to the size of a finger between two knuckles
Wow it's cold out, I can barely see my dick, it must be knuckling up.

I don't have a micropenis, it's just knuckling up!
by Nasbaby December 15, 2010
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to prepare to fight.
Guy 1 "i was at the bar chillin talkin to this girl after the band played, then this dude looked at me like he wanted a problem."

Guy 2 "what happened?"

Guy 1 "I had to knuckle up then his boy pulled him back."
by J Fri May 11, 2008
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