Definitions by Cruel Leader

niii 

a slang term for "nice", used interchangeably with "sweet" or "cool". Usually drawn out in speech and pronounced "n iiiiiii eeeeee"

Mike: "Dude those are some niii pics you got there from your backpacking trip."

Teacher: "No homework this weekend, class."
Student: "Niiiiiiiii!"

niii by Cruel Leader March 1, 2010