Definition & Meaning of "knocker"in English

What is the origin of the term "knocker" and how is it used?

Knocker is a slang term that appeared in early–mid 20th-century English to refer to a woman's breast. The term comes from the idea of something round or prominent that can be "knocked" against, following a pattern in English slang of using everyday actions or objects to describe body parts. Historically, it was informal and sometimes playful, but it could also be crude or sexualized depending on context. Today it remains colloquial and slightly vulgar, generally used in casual, joking, or sexualized speech rather than polite or neutral conversation.