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1.
Someone who is both Jewish and genius.
Keyne: I'm a fuckin genius!

Shawn: No, you're a jewnius.

Ben: You're fuckin right doggie!
by The Goofather March 25, 2008
 
2.
A very smart Jewish person, or a "jewish genius." Usually used to describe a jewish person sarcastically when they are being less than intelligent.
Jeremy is a jewnius for taking a shot on his own basket.

Jillian is a jewnius for taking that much adderall.
by francis4thewin October 25, 2009
 
3.
A genius but they are Jewish so it only makes sense to call them JEWnius.
Gabe: 12x14 = 168
Jake= OMFG how did u know that u JEWnius
by Anonymous Pubes January 19, 2012
 
4.
a form of genius, but one who specifically knows all about jews and their heritage.
That kid singing all the prayers, hes a jewnius.
by chocoluvr1234567890 May 15, 2009