- (also door knocker)[countable]
a metal object attached to the outside of the door of a house, etc. that you hit against the door to attract attention （固定在门上供敲门用的）门环 
- [countable] (informal)
a person who is always criticizing somebody/something 吹毛求疵的人；一味批评的人 - knockers[plural] (taboo, slang)
an offensive word for a woman’s breasts （冒犯语）乳房，奶子
