Not a decade, but a term for a 9 year span

Question

Thanks for the help in advance; first time posting here.

I'm curious what the most appropriate single word is to describe a 9 year time span, or a 9 year anniversary. A search on Google didn't turn up much, but it did help me find this information in the Wiki page for "decade": "...Other words for spans of years also come from Latin: biennium (2 years), triennium (3 years), quadrennium (4 years), lustrum (5 years)".

Following this pattern, the most appropriate form of the word I could come up with is novemnium, seeing as novem is Latin for 9. Is this the correct structure/spelling, or are there better alternatives to this problem?

Answer 1

The noun form of user's answer (novennial), and I believe you are looking for a noun, is novennium

(rare) A nine-year period or cycle.

From Wiktionary

Also see enneatic:

Occurring once in every nine times, days, years, etc.; every ninth.

From The Free Dictionary

And finally, enneaeteric

Containing or consisting of nine years: as, an enneaeteric period.

From Wordnik, in turn from The Century Dictionary

Answer 2

You had the right idea. Leave out the first "m" an use it as an adjective. The word you are seeking is "novennial".

https://www.thefreedictionary.com/Novennial

Answer 3

Because there is no zero year, the first “decade” of AD and the last “decade” of BC only have nine years. Since these are sets of nine years, they should be called Nonades, on the model of Decade. In French, a set of nine objects is called a nonade (though not pronounced with a long A). In English this is called a nonad. For a nine year time period, we should use nonade with a long A.