Nipple

n.
  1. (Anat.) The protuberance through which milk is drawn from the breast or mamma; the mammilla; a teat; a pap.
  2. The orifice at which any animal liquid, as the oil from an oil bag, is discharged.
  3. Any small projection or article in which there is an orifice for discharging a fluid, or for other purposes; as, the nipple of a nursing bottle; the nipple of a percussion lock, or that part on which the cap is put and through which the fire passes to the charge.
  4. (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.
    5. Solder nipple ,
    a short pipe, usually of brass, one end of which is tapered and adapted for attachment to the end of a lead pipe by soldering.