The title of this question says it all.
Are there nouns for longer periods than a millennium ?

I mean words designating a specific number of years.

Era, age and epoch don't count as they just indicate a period of time (possibly quite long) that is not counted in years, but that is defined by of a characteristic of that period.
(E.g the "Age of the Dinosaurs" was a fair number of millions of years, but not a specific number.)

  • Scientists in many disciplines routinely refer to megayears and gigayears these days. And that's not to mention terayears and petayears. Commented Jun 6, 2018 at 15:49
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    Note also that the term “epoch” in both computing and astronomy refers to a specific reference time and not to a period of time. There is potential for confusion unless you are careful.
    – Mike Scott
    Commented Sep 7, 2020 at 19:02

6 Answers 6


There is presently nothing that comes next.

Some terms referenced do have year values assigned to them (Epoch at 1,000,000 years and Aeon at 1,000,000,000 years) but common usage relates to geological time periods which are not consistent in length.

Once beyond millennia we use numbers of years such as "One Hundred-Thousand Years", or some use metric prefixes to 'annum' (for example megaannum as referenced in Wikipedia) but they are basically the same idea. To follow the same principle from a Latin root form (as Decade, Century etc are latin) then `Decem millennium' (10,000 years) would arguably be closest to our existing words but it would be unlikely to see common use.

  • I wasn't aware of "annum". Now that I am, I can't but help wondering if this would be understood by a the general public. I certainly haven't heard/seen this before. I asked a friend who is a professional interpreter/translator and she didn't know the term either.
    – Tonny
    Commented Jan 11, 2016 at 15:47
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    @Tonny - No, "annum" is not a common term, particularly in the way it's used in "megaannum". I would say don't use it when writing for the general public.
    – stangdon
    Commented Jan 11, 2016 at 15:58
  • People say, “per annum”, and I would expect the general population to understand that it means “one year”. As part of a compound word, it’s likely to stump people. Commented Mar 18, 2018 at 15:35
  • Digging on en.wikipedia.org/wiki/…, I found these words (epoch, eon), but the amount of years suggested is extremely widespread
    – Nato Boram
    Commented Sep 5, 2022 at 2:26

The next stop after millennium is terasecond
For rounded number of years, it's megaannum

An interesting table can be found here

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    Can't find the table as of 2023. Note to future posters: please post a screenshot, as this will happen again.
    – Chrisuu
    Commented Mar 6, 2023 at 18:01

Acccumulation is correct: the word myriad technically meant 10,000 and could be useful in 8,000 or so years.


The answer is Eon. Eon often refers to a span of one billion years.


A “Terasecond” is a word which refers to a period of time lasting 31, 700yrs


The word "myriad" is often used to just mean "large number", but technically means 10,000. It doesn't specifically mean "10,000 years", but it could be used in that context. "Myriayear" would mean "10,000 years", but is unlikely to be understood.

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