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2.
Unno is the latest in a long line of Proper English words unwillingfully sodomised so that they are fit for internet consumption.
jayseven: Unno watya onboot teh dud!
jayseven's dad: I don't know what you're on about, son!
by jayseven July 28, 2004
 
1.
Same meaning as "dunno", which comes from "don't know", except it's shorter and easier to type when IMing
Guy: what time is the party at josh's house?
Girl: i unno, go ask stephanie
by krystal_kiss February 16, 2006