nipple

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The small projection near the center of the mammary gland containing the outlets of the milk ducts through which young mammals obtain milk from the adult female; a teat.
2. n. A corresponding projection of the male breast.
3. n. The rubber cap on a bottle from which a baby nurses.
4. n. A pacifier for an infant.
5. n. Any of various devices functioning like or resembling a nipple, especially:
6. n. A regulated opening for discharging a liquid, as in a small stopcock.
7. n. A pipe coupling threaded on both ends.
8. n. A short extension of pipe to which a nozzle can be attached.
9. n. A small projection through which grease in a grease gun can be forced into a bearing.
10. n. A natural or geographic projection resembling a nipple, as a mountain crest.

Century Dictionary and Cyclopedia

1. n. A protuberance of the breast where, in the female, the galactophorous ducts discharge; a pap; a teat.
2. n. The papilla by which any animal secretion is discharged.
3. n. Anything that projects like a nipple, as the projecting piece in a gun or a cartridge upon which the percussion-cap is placed to be struck by the hammer, the mouthpiece of a nursing-bottle, a nipple-shield, etc.
4. n. A reducing-coupling for hose or for joining a hose to a pipe. It is often threaded or grooved on the outside to facilitate the making of a tight joint by means of a wire binding, compressing the hose into the indentations.
5. n. A hollow piece projecting from and forming a passage connecting with the interior of a metal pipe, used for the attachment of a faucet or cock.
6. To furnish with a nipple or nipples; cover with nipple-like protuberances.

Wiktionary

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

GNU Webster's 1913

1. n. (Anat.) The protuberance through which milk is drawn from the breast or mamma; the mammilla; a teat; a pap.
2. n. rare The orifice at which any animal liquid, as the oil from an oil bag, is discharged.
3. n. Any small projection or article in which there is an orifice for discharging a fluid, or for other purposes
4. n. (Mech.) A pipe fitting, consisting of a short piece of pipe, usually provided with a screw thread at each end, for connecting two other fittings.

WordNet 3.0

1. n. a flexible cap on a baby's feeding bottle or pacifier
2. n. the small projection of a mammary gland