Sacré bleu!

Blue humour, blue movies, blue talk—what’s so obscene about the colour blue?

Nobody really knows, as it turns out. The origin of blue in the sense of lewd, coarse, or pornographic has been tough to pin down: etymologists have put forward a bunch of theories but haven’t found anything conclusive.

The Oxford English Dictionary’s earliest example of this usage dates back to 1818, in John Mitford’s The Adventures of Johnny Newcome in the Navy, in which Mitford (under pseudonym Alfred Burton) wrote, “Blush, Pluto! Blush as brimstone blue! This bluer Town can boast like you A ‘facilis descensus’ too.” I can’t find evidence that this blue-as-brimstone metaphor for sin really caught on, though. John Mactaggart’s Scottish Gallovidian Encyclopediafrom 1824, lists “Thread o’Blue” to mean “any little smutty touch in song-singing, chatting, or piece of writing,” which sounds more like the blue we’re after, but the encyclopedia doesn’t give any hints about its origins. In Slang and Its Analogues Past and Present (1890), John Stephen Farmer and William Ernest Henley proposed that blue might refer to the blue gown worn by a convicted prostitute in a house of correction, although that usage dates from the sixteenth century and doesn’t seem to have endured into the early 1800s. A related source for the crass blue is the colour’s association in Britain with uniforms worn by servants and licensed beggars, who were not necessarily smutty but were certainly considered coarse and unrefined, paralleling the evolution of the term blue collar, which popped up in North America in the twentieth century.

Slang authority John Camden Hotten, in his 1859 publication, A Dictionary of Modern Slang, Cant, and Vulgar Words, suggested that the base or indecent connotation of blue had its origins in the French Bibliothèque bleue, popular literature published between the early-seventeenth and mid-eighteenth centuries on low-quality paper with a blue cover and read by the lower classes. The OED disputes this conjecture, “since such material appears in general to have been highly moral in tone”—unlike, say, the blue books that emerged in Storyville, New Orleans’s red-light district, which were directories of the area’s prostitution services.

Whether swearing a blue streak has different origins compared with blue talk or blue language (not to be confused with Léon Bollack’s constructed language) is also up for debate. Blue streak may originally have simply meant fast or vivid, like a flash of lightning: an issue of The Kentuckian from 1830 featured the sentence “To pass…with such rapidity as not even to leave a ‘blue streak’ behind him.” Swearing had wormed its way into the expression by 1847, as in “a ‘blue streak’ of oaths,” possibly independently of other sweary instances of blue.

Blue laws, which began in 1755 as puritanical restrictions on the activities of New England residents on Sundays, are unconnected with the obscene sense of blue. Contrary to popular belief, blue laws were never printed on blue paper and so the origin of their name also remains a mystery.

The term off-colour evolved separately, appearing in the mid-nineteenth century. According to the OED, it was first used to describe diamonds of lower clarity and thus took on the connotation of impure. I can’t find anything to suggest that off-colour = blue.

While we’re at it, I should also mention that sacré bleu (or sacrebleu) isn’t an oath French speakers use (anymore). And even this interjection has a murky etymology. Depending on whom you ask, bleu might refer to the Virgin Mary, often depicted wearing a blue dress or sash, or it might be a mincing of dieu (God). I’m inclined to believe the latter, because other dieu bleu minced oaths—including corbleu (for corps de dieu, or God’s body) and morbleu (for mort de dieu, or God’s death)—can be found in medieval French records.

The ribald blue is a bit of idiomatic language with a squishy, sordid history that I can’t offer you in a neat package—and is a great example of how equivocal etymology can be. If you’ve come across other theories about its origins, let us know in the comments.

19 thoughts on “Sacré bleu!

  1. Stan Carey May 21, 2015 / 3:12 pm

    I can’t find anything to suggest that off-colour = blue.

    The dress! The dress!

    Liked by 3 people

  2. Russell May 21, 2015 / 3:34 pm

    This is entirely speculation, but I wonder if it has anything to do with the term “bleu” for rarer-than-rare meat, since “raw” has a similar meaning.

    Liked by 1 person

  3. Joe Clark May 23, 2015 / 5:07 pm

    It’s sacre, not sacré. It’s a sure sign of an overconfident anglophone when they throw diacritics on everything in sight.

    Liked by 1 person

    • Iva Cheung May 23, 2015 / 5:45 pm

      1. Sacré means “sacred.” Sacré dieu, meaning “sacred God,” is minced to sacré bleu.
      2. In the post, I note that some people write sacré bleu as sacrebleu.
      3. I speak both English and French.

      Liked by 2 people

      • Joe Clark May 23, 2015 / 7:06 pm

        Sacre is a noun used adjectivally here. It’s sacre bleu.

        Liked by 1 person

    • Iva Cheung May 23, 2015 / 8:19 pm

      OK—I’ve looked into this a bit more, and I’m pretty sure it can be both.

      This entry ( shows that sacrebleu might have been a mincing of sacre Dieu or sacre de Dieu.

      But see also this entry on crebleu and crébleu (, which are clipped forms of the oath and which reflect variations in pronunciation. Definition B3 in particular shows sacré Dieu (and sacré nom de Dieu) was used “pour renforcer les jurons.”

      Can we be friends now?


  4. John Kelly May 23, 2015 / 5:44 pm

    And then we have blue balls, the color label probably due to, um and ew, vascular excitement?

    Liked by 1 person

    • Iva Cheung May 23, 2015 / 6:05 pm

      Yes! Blue balls were, uh, on my radar, but I figured the origins of that phrase were too obvious to fit within the theme of the post. So thanks for mentioning it!


  5. Debunker May 23, 2015 / 9:07 pm

    Another interesting line of enquiry might be that verde (green) is used in much the same way in Spanish. A viejo verde is a dirty old man.

    Liked by 1 person

  6. יובל פינטר May 26, 2015 / 8:29 am

    In Israeli Hebrew having “a blue head” means constantly thinking naughty thoughts. Among some nature-loving folk the etymology has spread that this derives from the indigenous Stellagama (xardon חרדון) whose head slightly changes its color when sexually aroused. The chances for this being real are of course slim to none.

    Liked by 1 person

    • Michael Billips August 14, 2019 / 5:20 pm

      OK so the name of a lizard whose head changes color when it gets turned on is called what essentially sounds like “hard on” to the English ear! Is this a phonologically statistical accident or is this scientists having fun as they do? (or I guess lay people could have coined that as the common name, don’t know enough here)


      • יובל פינטר August 15, 2019 / 3:18 pm

        Ah, I may have been unclear. There’s no phonological resemblance between the creature’s name and the term for horniness. The claimed etymology is purely semantic – “we say people with dirty thoughts are ‘blue-heads’ because of this animal whose head becomes blue in heat”.


  7. Bryan Geer May 31, 2015 / 3:51 pm

    Regarding “blue” material in stand-up comedy:

    Nineteenth-century American vaudeville entertainment was the “polite” alternative to burlesque, and vaudeville impresario B. F. Keith warned his performers to avoid the use of words like “Hell.”

    “Keith’s theater managers would occasionally send out blue envelopes with orders to omit certain suggestive lines of songs and possible substitutions for those words. If actors chose to ignore these orders or quit, they would … never again be allowed to work on the Keith Circuit.” (

    Thus, NEVER DO BLUE.

    Liked by 1 person

    • Iva Cheung May 31, 2015 / 5:05 pm

      B.F. Keith sounds like a big bag of fun.


  8. Jen May 3, 2019 / 7:57 pm

    Hmmmm…makes me wonder about Eiffel 65 – Blue and Blissco’s true intentions. Listen to the lyrics.


  9. Willem July 26, 2020 / 7:21 am

    The origin of blue being holy or devine may be taken from Mongolia, known as the land of the eternal blue sky, eternal refering to the devine, celestial etc.

    Liked by 1 person

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