Now that it's 29th of February, there is no way not to ask: What is a leap year in Latin?

Leap month and leap day (mensis/dies intercalaris or intercalarius) are well attested. In the Julian calendar a leap day is added every four years, whereas before Caesar's reform a whole month was added when needed. But is there a name for the year that contains an added month or day?

Annus intercalaris would make sense, but I fear that it might mean "an added year" rather than "a year with something added". Is there an established expression for a leap year in Latin of any era? What would be a reasonable way to express it?

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    llmavirta: Glosbe "leap year": "annus bisextus"; bisextus being an intercalary i.e. something inserted between other things: "annus intercalarius"; a year + additional day, "annus bisextilis". Unusually, for Glosbe, no attestations were offered. On Wiktionary, a quote from 1553 which ends: "...quartus vero, ex 366 diebus componitur, et bisextilis nuncupatur." = "...while the fourth (year), composed of 366 days, is called bissextile.). Pock. Ox. Dict. gives "bisextilis annus" (masculine). Is it your birthday, today? If so Happy Birthday; if not, please ignore this impertinence.
    – tony
    Commented Feb 29, 2020 at 11:44
  • Does Annus saltus seem reasonable?
    – Allawonder
    Commented Mar 1, 2020 at 19:54
  • @Allawonder Possibly, but you'd have to argue why it makes sense. I don't recall seeing that in Latin. It looks like a direct translation from English, and not all languages relate leap years to jumping. But whatever the reasoning might be, I'd be happy to see it fleshed out as an answer.
    – Joonas Ilmavirta
    Commented Mar 1, 2020 at 20:48

3 Answers 3


As for the Gregorian calendar, the source is indeed (Ecclesiastical) Latin:

Deinde, ne in posterum a XII Kalendas Aprilis æquinoctium recedat, statuimus bissextum quarto quoque anno (uti mos est) continuari debere, præterquam in centesimis annis; qui, quamvis bissextiles antea semper fuerint, qualem etiam esse volumus annum MDC, post eum tamen qui deinceps consequentur centesimi non omnes bissextiles sint, sed in quadringentis quibusque annis primi quique tres centesimi sine bissexto transigantur, quartus vero quisque centesimus bissextilis sit, ita ut annus MDCC, MDCCC, MDCCCC bissextiles non sint. Anno vero MM, more consueto dies bissextus intercaletur, Februario dies XXIX continente, idemque ordo intermittendi intercalandique bissextum diem in quadringentis quibusque annis perpetuo conservetur. (Inter Gravissimas, 9).

Inter Gravissimas is the papal bull that established the current (i.e., Gregorian) calendar.

English translation by Spencer (1999):

Then, lest the equinox recede from XII calends April [March 21st] in the future, we establish every fourth year to be bissextile (as the custom is), except in centennial years ; which always were bissextile until now; we wish that year 1600 is still bissextile; after that, however, those centennial years that follow are not all bissextile, but in each four hundred years, the first three centennial years are not bissextile, and the fourth centennial year, however, is bissextile, so the years 1700, 1800 and 1900 will not be bissextile. Assuredly, the year 2000, as with our custom, will have a bissextile intercalation, February will contain 29 days, and the same rule of intermittent bissextile intercalations in each four hundred year period will be preserved in perpetuity.

Both the original Latin text and English translation (and also one to French) may be found here.

Here we see both bissextus and bissextilis. It seems to me that the former is preferred for the day and the latter for the year. (For this to be true, the translation of the relevant portion of the first sentence would be something like we establish that there must continue to be a leap day every four years.)

Addendum: As pointed by Vincenzo Oliva and tchrist in the comments, it is worth noting that bissextus literally means twice-sixth, as it was originally used to designate the intercalary day in the Julian calendar, that Julius decided to be the repetition (hence bis-) of the sixth day before the kalends of March (i.e., the 24th of February).

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    Side comment: this also adds to the answer of this question
    – Rafael
    Commented Feb 29, 2020 at 17:20
  • 3
    +1. Note that the terms have Roman origins, related to the original Roman calendar. See here, perhaps you could summarize and integrate this in your answer. Commented Feb 29, 2020 at 17:41
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    @VincenzoOliva Agree that it’s worth explaining why Caesar’s bissext (a largely forgotten and obsolete word in English today, though bissextile remains) was actually a “double-sixth” day before the March Kalends and so was considered to double the 24ᵗʰ of February rather than the 28ᵗʰ as we would now reckon it.
    – tchrist
    Commented Feb 29, 2020 at 19:32
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    just wanted to mention that the Russian word високосный for "leap (year)" originates from "bissextus"
    – Quassnoi
    Commented Feb 29, 2020 at 20:20
  • Bissextile is a great word, but pretty much obsolete in English, at least according to google ngrams Commented Mar 1, 2020 at 16:33

According to the Neo-Latin Lexicon a leap year is annus intercalaris or annus bisextilis.


The Roman annus bisextilis (bisextile year) has an extra day (bis VI Kal Mar = 24 February) preceding VI Kal Mar = 25 February. Hence its name.

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