A nipple is a short length of pipe with threads at each end. This nipple is used to join couplings or fittings. Used in plumbing!
A nipple is 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. This nipple is a teat.
A nipple is the rubber cap on a bottle from which a baby nurses. This nipple is a pacifier for an infant.
A nipple is regulated opening for discharging a liquid, as in a small stopcock.
A nipple is natural or geographic projection resembling a nipple. This nipple iss a mountain crest.
A grease nipple is a lubrication fitting used in mechanical systems to add grease with a grease gun.