either of the two small round dark parts on a person’s chest. Babies can drink milk from their mother’s breasts through the nipples. 乳头 
Oxford Collocations Dictionaryadjective- erect
- hard
- swollen
- …
- pinch
- suck
- squeeze
- …
- harden
- (North American English) (British English teat)
the rubber part at the end of a baby’s bottle that the baby sucks on with its lips and tongue in order to get milk, etc. from the bottle 奶嘴；橡胶乳头 a small metal, plastic or rubber object that is like a nipple in shape with a small hole in the end, especially one that is used as part of a machine to direct oil, etc. into a particular place 乳头状物品；（机器的）喷嘴 a grease nipple 油脂枪喷嘴
Word Originmid 16th cent. (also as neble, nible): perhaps a diminutive of neb.