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1.
a stoner with no life or future.
Don't shmoke dat grass man, you gonna turn into an isnt!
by the population of earth July 06, 2006
 
2.
referring to a bulbous sexual organ, which all heterosexual men find attractive, or in reference to a specific sexual action that one would perform on another.
Give me one good reason as to why I should "isnt" all over her back.
by the boy who was once an isnt April 07, 2011
 
3.
A slang term for the perineum.
Whilst in the heat of passion you may ask your partner to lick your isn't.

What is your isn't? She asks

It's that bit which isn't my arse, and isn't my balls you may reply!!!
by blackninja980 September 21, 2007