as a verb: to grab and tug a nipple, especially through clothing, especially roughly; in bdsm, a common way to find out if the girl you're making out with is really a sub or just playing in the scene.
I was making out with Megan and I nippled her real good while we were kissing; she started humping my leg so I knew she was one of us.
1) That precious spot in a female breast. Most of the times it could be brown. Males like to lick and suck on them. They also are used to feed a new born baby.
2) A nipple can also be that part of a babys drinking bottle they drink the fluids out of.