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, blasphemies, terms relating to Hell or damnation when used outside of religious contexts, or slurs. The "four-letter" claim refers to the fact that many (but not all) English "swear words" are incidentally four-character monosyllables. This description came into use during the first half of the twentieth century.