four-letter word, n. phr.
Short words that are vulgar (offensive language such as swearing and language about sex). This idiom is a polite way to refer to impolite language. An older, related idiom was four-letter man, which meant "an obnoxious man," one who would use such language. Four-letter word was recorded as early as 1934.
• Billy got into trouble at school for using a four-letter word in front of his teacher.
• Our general manager is often heard using four-letter words around the office.
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