knocker
noun [ C ] uk/ˈnɒk.ər/ us/ˈnɑː.kɚ/
(METAL OBJECT)
(also doorknocker)（装在门上供人敲门用的）门环
a metal object attached to a door that visitors use to hit the door in order to attract attention
(CRITIC)
UK informal disapproving吹毛求疵的人，一味批评的人
a person who is always criticizing someone or something
(BREASTS)
knockers[ plural ] slang （冒犯性用语）乳房，奶子
a woman's breasts. Some people consider this word offensive.