Etymology From earlier neple, nypil, neble, believed to be a diminutive of nib, neb (“tip, point”), equivalent to nib + -le. Compare Old English nypel (“elephant trunk”), formed analogously as "a protuberance from one's neb" .
Anatomy, Medicine, Sciences The projection of a mammary gland from which, on female therian mammals, milk is secreted.
Mary felt annoyed at the girl; just because bras had become passé, did a girl with so pronounced a bosom have to cater to fashion? In this case practicality dictated a bra, and Mary stood at the desk feeling herself flushing with disapproval. And artificial nipple-dilation; it was just too much.1964, Philip K. Dick, “THREE”, in Clans of the Alphane Moon, United States: Ace Books, →OCLC; republished London: HarperCollinsPublishers, 1996, →ISBN, page 27:
2
The nipple (noun sense 1) and the areola together.
Joan Trieste wore skin-tight dark pants and slippers and a cotton man’s-style shirt; as far as he could tell, she had on no bra, as fashion dictated, but her nipples were merely flat dark circles beneath the white cotton fabric of her shirt: she could not afford or did not care to have the currently-popular dilation operation.1964, Philip K. Dick, “FOUR”, in Clans of the Alphane Moon, United States: Ace Books, →OCLC; republished London: HarperCollinsPublishers, 1996, →ISBN, page 37:
3
A mechanical device through which liquids or gases can be passed in a regulated manner.
4
An artificial nipple (noun sense 1) used for bottle-feeding infants.
5
Any small physical protrusion, such as the lumps on the F and J keys on computer keyboards.
6
Any small physical protrusion on an automotive, a machine part or any other part that fits into a groove on another part.
7
Historical A perforated segment that fits into part of the breech of a muzzle-loading gun, on which the percussion cap is fixed.
I could tell he didn't agree but he went to the corner and took up his squirrel gun, feeling the nipple for a percussion cap.2013, Philipp Meyer, The Son, Simon & Schuster, published 2014, page 23:
Cycling, Hobbies, Lifestyle, Sports An internally threaded piece which holds a bicycle spoke in place on the rim.
Turn the nipples on to the bicycle spokes only one turn, for each spoke on the new wheel all the way around until they are all snug, then check alignment.
These were first constructed by heading the spokes, threading them through a steel felloe or rim and inserting them into screwed nipples which were in their turn screwed into the flanges of the hub.1921, W. F. Grew, The Cycle Industry, London, page 5:
Etymology From earlier neple, nypil, neble, believed to be a diminutive of nib, neb (“tip, point”), equivalent to nib + -le. Compare Old English nypel (“elephant trunk”), formed analogously as "a protuberance from one's neb" .
1
To fit (a baby's bottle, etc.) with a nipple.
2
To give one's nipple to (a baby) to allow breastfeeding.