Four-letter word

The phrase four-letter word refers to a set of English-language words written with four letters which are considered profane, including common popular or slang terms for excretory functions, sexual activity and genitalia, and (depending on the listener/reader) sometimes also certain terms relating to Hell and/or damnation when used outside their original religious context(s), and/or slurs. The "four-letter" claim refers to the fact that a large number of (but not all) English "swear words" are incidentally four-character monosyllables. This description came into use during the first half of the twentieth century.