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1.
homeboy; homie; --always said to a close friend that happens to be a white male

In reference to a white person's desire to say "nigga" when talking gansta and for their wafer-like appearance.
"Yo, Tim. What is is?"
"Shit, necco...I'm just trying to mack on these skeezers and skallywags. You know how we do it."
by TallCan211 May 19, 2009
 
2.
Once the name for the chalk like candy that candy hearts are made from, now a term referring to nipples.
"Owww, quit pinching my neccos!"
by Vegetable Man December 07, 2004