knock·er
noun/ˈnɒkə(r)/
/ˈnɑːkər/
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(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 Topics Houses and homesc2(装在门上供敲门用的)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) a woman’s breasts
(女人的)乳房,奶子