An answer to an earlier question about age of wine introduced me to adjectives for specific ages in years. Similarly, there are nouns for periods of time in years. For example:

  1. bimus & biennium
  2. trimus & triennium
  3. quadrimus & quadriennium

Number 1 is expectedly exceptional, and the corresponding words would be anniculus and annus. All these words are mentioned in Lewis and Short.

How far do numbers of this kind extend? It is somewhat laborious to guess more words of this kind and check dictionaries for their existence; a list of all — or most or many — attested forms would be nice. Can such words be derived productively, and if yes, how do I do it?

My guess is that such words exist for 2–10, 100, and 1000, but not for other numbers.

Side note: If you think this question should rather be split in two (one for bimus etc. and one for biennium etc.), I can do that.

  • Relevant comic: xkcd.com/1602
    – blagae
    Jun 20, 2017 at 14:01
  • @blagae This site will soon complete its first sesquiennium. Does it mean we should meet up to celebrate?
    – Joonas Ilmavirta
    Jun 20, 2017 at 14:07

1 Answer 1


A simple search for words ending in -ennium will give you a list of year-counting words attested by Lewis & Short (excluding one false positive):

2 - biennium
3 - triennium
4 - quadriennium
5 - quinquennium
6 - sexennium
7 - septuennium, septennium
8 - octennium
10 - decennium
12 - duodecennium, duodennium
20 - vicennium
30 - tricennium

-ennis is the corresponding adjective ending, and also has many examples. Excluding periods already in the above list, we can add from L&S:

9 - novennis
? - quotennis
∞ - perennis

Later Latin has many other examples (novennium, millennium, etc.). English (and, I'm sure, other modern languages) has even spoken of a sesquicentennium (=150).

All this suggests that the construction is only restricted by the writer's and audience's tolerance for ever increasing complexity. At some point, centum quadraginta tres annos makes more sense than centumquadragintatriennium. I suspect the latter would be understood, though.

Latin also offers the ability to multiply these time periods. Lewis & Short cites Macrobius (5th c.), who uses:

tertio quoque octennio (Macr. S. 1, 13, 13)

This means, "every third eight-year period" = "every 24 years."

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