Tous les trente-six du mois

Once in a blue moon
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French Expression

Meaning once in a blue moon
Literally the 36th of every month
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Pronunciation French sound files [too lay tra(n)t(eu) sees du mwah]
IPA   [tu le tʀãt sis dy mwa]

Usage notes: In reference to something that happens very rarely, English speakers say "once in a blue moon." There’s a blue moon (une lune bleue) on average once every two to three years,* so this is a poetic and fairly logical expression.

The equivalent French expression is tous les trente-six du mois, which I’ve always found very odd. There’s no such thing as a month with 36 days (at least not on this planet), so the 36th of the month is nonsense – shouldn’t that mean "never" rather than "rarely"? In fact, it does mean "never" in the same exaggerative way that word is used in English.

Par exemple…

Tu ne m’ecris que tous les 36 du mois !   You never write to me! (OK, not never, but only twice in the last year.)
You only write to me once in a blue moon!
Mon mari fait la vaisselle tous les 36 du mois.   My husband does the dishes once in a blue moon.

* There are two potential meanings for "blue moon" – learn more.

More expressions with trente-six

Trente-six is used informally to mean "a whole bunch" in several other expressions:

  • Il y a en a trente-six modèles – There are umpteen models
  • Il n’y a pas trente-six possibilités / solutions – There aren’t that many possibilities / solutions
  • avoir trente-six mille choses à faire – to have a million things to do
  • être dans le trente-sixième dessous – to be very depressed
  • faire trente-six choses à la fois / en même temps – to (try to) do a hundred things at the same time
  • se mettre sur son trente-six –> se mettre sur son trente et un
  • voir trente-six chandelles (informal) – to see stars, be knocked out

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Tous les 36 du mois

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