four-letter word

From the frequency of the most common swear words being composed of or spelt with four letters.

four-letter word (plural four-letter words)

1. A reference to any of several of the strongest English swear words that are also four letters long, especially those composing the so-called seven dirty words.
   • 1934, Cole Porter (lyrics and music), “Anything Goes”, in Anything Goes:

     Good authors, too, who once knew better words / Now only use four-letter words

   • 1981, “Wordy Rappinghood”, performed by Tom Tom Club:

     Words can make you pay and pay / Four-letter words I cannot say

2. (by extension) A swear word or any words considered to be taboo in a given scenario (regardless of length of word).
   • 1968, “Work Is a Four-Letter Word”, performed by Cilla Black:

     People say that you were born lazy / because you think that work is four-letter word

   • 1996, “Friend Is a Four-Letter Word”, in Fashion Nugget, performed by Cake:

     To me, coming from you, 'Friend' is a four letter word

   • 2018 January 20, Eve Smith, “The techlash against Amazon, Facebook and Google—and what they can do”, in The Economist‎^[1]:

     “Tech” is not yet a four-letter word, but it could soon become one.

•   four-letter word on Wikipedia.Wikipedia