I'm working on a calendar. To choose the name of the months I focused on Latin and in particular on a systematisation of the names finishing with 'ber'. I was wondering if my choices were correct and realistic. For example, the name of the twelfth month is too long so if you think you know how it would have evolved in English, I'm interested.

  1. Premember
  2. Secember
  3. Tertiember
  4. Quatember
  5. Quintember
  6. Sextember
  7. September
  8. October
  9. November
  10. December
  11. Undecember
  12. Duodecember

2 Answers 2


In addition to the familiar September–December, there were two more numerically named months before they were renamed in early imperial era: Quintilis and Sextilis. These should definitely go to your slots 5 and 6. In English you could call these Quintile and Sextile.

You seem to have slightly misanalyzed the ending. What you add to the end of a number is not -ember but -ber. This is an easy mistake to make, as three of the four usual month numbers (septem, octo, novem, decem) end in -em. The key observation is that we have October, not Octember.

It appears that the numbers 7–10 get the ending -ber to the cardinal number, whereas 5–6 get the ending -ilis to the (stem of the) ordinal number. That is, Quin(c)tilis and Sextilis seem to be based on quintus and sextus, not quinque and sex. So, there are two attested ways to produce month names from numbers.

To me it sounds more natural to use the ordinal one for the first months:

  1. primus > Primilis
  2. secundus/alter > Secundilis/Altrilis
  3. tertius > Tertilis (somehow Tertiilis sounds unnatural)
  4. quartus > Quartilis

Tertilis and Quartilis (or Tertile and Quartile in English) sound quite natural to me, but the first two less so. However, they feel more understandable and Latin to me than the ones you proposed. With this pattern the first half of the year has -ilis, the second half has -ber.

I find no way around the somewhat clumsy Undecember and Duodecember. As Draconis points out in another answer, the Latin numbers 11 and 12 are undecim and duodecim, so maybe you could change the month names to Undecimber and Duodecimber. However, it would not be unreasonable to keep the -e- by analogy in the English versions. I don't know whether adding -ber in Latin would change the vowel or whether later developments in English would naturally lead to a vowel change, but this is just a minor detail. One practical benefit of the -i- is that it sets the eleventh and twelfth month apart from December. The names undecimber and duodecimber are used for the thirteenth and fourteenth month in some contexts, such as computing.

An option worth serious consideration is having the year start in March instead of January. This is what the Roman calendar did, and this is why the names are off by two. This would have the benefit of the months names aligning with the ones already in use.

Here is the suggested list in English resulting from the considerations above:

  1. Primile
  2. Altrile or Secundile
  3. Tertile
  4. Quartile
  5. Quintile
  6. Sextile
  7. September
  8. October
  9. November
  10. December
  11. Undecember or Undecimber
  12. Duodecember or Duodecimber
  • 2
    In computing, the thirteenth month is called UNDECIMBER. It is used to give an easy way to refer to (and thus specify) the names of months in calendars in which a year has thirteen months - or in which some years do. [This Wikipedia article is concise and reasonably sensible][1] [1]: en.m.wikipedia.org/wiki/Undecimber Commented Dec 11, 2022 at 11:12

To supplement Joonas's wonderful answer, the words for "eleven" and "twelve" in Latin are undecim and duodecim, with an i. So I would suggest those months be changed to Undecimber and Duodecimber.

  • Good point! I upgraded my answer a bit. I would find it reasonable to keep the e in the English versions by analogy. I don't really know whether the -ber would have an effect on the vowel in Latin.
    – Joonas Ilmavirta
    Commented Mar 31, 2019 at 18:49
  • 1
    I would strongly prefer "Undecember" and "Duodecember" rather than using forms ending in "-decimber", both because of the analogy of "September", &al., and the fact the reduction of the "e" to "i" in undecim would not naturally occur in a heavy syllable, as in Undec(e/i)mber.
    – varro
    Commented Apr 1, 2019 at 3:31
  • @varro Does vowel reduction not happen in heavy syllables? I thought it happened to short vowels no matter what came after them.
    – Draconis
    Commented Apr 1, 2019 at 17:42
  • 2
    I probably should have been more precise in my comment. Compare accipere with acceptus - the second vowel in each exhibits a type of vowel reduction, but the closed syllable in acceptus prevents the last stage in the full progression of /a/ -> /e/ -> /i/, which is at issue here. That said, the various numbers ending in -decim seem to be somewhat irregular in that we should expect to see forms such as *undicem, &c. rather than undecim.
    – varro
    Commented Apr 1, 2019 at 19:12

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