- 1either of the two small, round, dark parts on a person's chest. Babies can suck milk from their mother's breasts through the nipples.
- 2 the rubber part at the end of a baby's bottle that the baby sucks in order to get milk, etc. from the bottle
- 3a small metal, plastic, or rubber object that is shaped like a nipple with a small hole in the end, especially one that is used as part of a machine to direct oil, etc. into a particular place a grease nipple