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, terms relating to Hell or damnation when used outside of religious contexts 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.
Common four-letter words (in this sense) that are widely considered vulgar or offensive to a notable degree include: , (and regional variants such as feck, fick and foak), (or gism), , , and . Piss (formerly an offensive swear word) in particular, however, may be used in non-excretory contexts (pissed off, i.e. "angry", in US English and British UK English ; pissed, i.e. "drunk" in UK English) that are often not considered particularly offensive, and the word also occurs several times with its excretory meaning in the King James Bible. Several of these have been declared legally indecent under the United States Federal Communications Commission (FCC) TV and radio open-airwave broadcasting regulations.
A number of additional words of this length are upsetting to some, for religious or personal sensitivity reasons, such as: (UK), , , , , , and (UK). Racist, ableist, and slurs pertaining to an individual's sexual orientation may also qualify, such as (in the UK not a racial slur, but short for Mongol, or someone with Down's Syndrome - previously called Mongolism), , , , , and . Several "four-letter words" have multiple meanings (some even serving as given names), and usually only offend when used in their vulgar senses, for example: , , , , , (UK) and (UK). A borderline category includes words that are euphemistic evasions of "stronger" words, as well as those that happen to be short and have both an expletive sound to some listeners as well as a sexual or excretory meaning (many also have other, non-vulgar meanings): (US), , , , , (US), (UK, NZ, AUS), and , as several examples. Finally, certain four-lettered terms with limited usage can be considered offensive by some, within the regional dialect in which they are used, such as and .