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1.
a nun that, in a secret personal life, kicks ass by using anything from throwing stars to nunchucks
Woah, was that a nun that just beat that guy down?

No my friend: that was a nunja
by Yanty January 05, 2006
 
2.
An awesome person, who is way better than ninja, because only the best people get to be nunjas.
"Damn, she's ninja"

"No, she's better than that, she's nunja"
by SpEcTaCuLaR=] May 22, 2009
 
3.
A term used when one prefers to jokingly convey a response meaning "none of your business".

Also the exact phrase of origin.

Person 1 "Hey Wahtcha doing over there?"
Person 2 "Nunja.
Person 1 "Nunnja, what's that?"
Person 2 "Nunja god damn business!"
by SSPprod September 18, 2008