noun

1. the small protuberance on a breast or udder through which, in the female, the milk passes in suckling the young; teat
2. an artificial teatlike part, as of rubber, in the cap of a baby's nursing bottle
3. any projection, part, or thing resembling the nipple of a breast in shape or function; specif.,
   1. a short piece of pipe with both ends threaded
   2. a projection with a small opening through which a liquid or grease can be forced

Etymology: earlier neble, prob. dim. of neb