Nipples

noun

1. The projection of a mammary gland from which, on female mammals, milk is secreted.
2. A mechanical device through which liquids or gases can be passed in a regulated manner.
3. An artificial nipple (definition 1) used for bottle-feeding infants.
4. Any small physical protrusion, such as the lumps on the F and J keys on computer keyboards.
5. Any small physical protrusion on an automotive, a machine part or any other part that fits into a groove on another part.