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Obviously every year is annual. Every two years is biennial. Does the English language have a term for every 18 months?

RegDwigнt
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planetjones
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2 Answers2

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sesquiennial

ocurring every year and a half.

Etymology: semi ("half") + que ("and")

I cannot find a dictionary definition of this other than Wiktionary, and 0 hits on Google NGram.

But there are some examples of usage here

FAME now has responsibility for the sesquiennial (every 18 months) Music Festivals which attract players from Europe, American continent

JoseK
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    thank you JoseK - although my girlfriend is now debating whether it's an acceptable phrase to use in a document at work! – planetjones Jun 07 '11 at 10:47
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    @planetjones: Well, he answered to your question. If are not comfortable using "sesquiennial", just use "every 18 months", it's not that bad. :D @JoseK: Where did you find it? :D ahah +1 – Alenanno Jun 07 '11 at 10:48
  • @planetjones: Well, I only learnt this while researching your answer - dictionary.com asks "Did you mean sexennial?" I'll say this will have people searching in the dictionary for the meaning - so they'll have learnt something too. – JoseK Jun 07 '11 at 10:52
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    @Alennano: I picked up sesquicentennial (which means 150 years) listed on Wikipedia and did a guess search for sesquiennial – JoseK Jun 07 '11 at 10:55
  • @JoseK I see... Why everyone misspells my name the same way :D I need to investigate lol it can't be a coincidence. XD – Alenanno Jun 07 '11 at 11:03
  • I didn't find any source about how it pronounce, would be nice to add if someone finds anything. – Gigili Jun 07 '11 at 11:23
  • @Alenanno: oh man, sorry about that – JoseK Jun 07 '11 at 11:33
  • @JoseK, it's ok, no worries! – Alenanno Jun 07 '11 at 11:50
  • Alen is a unit of measure in Danish and with the postfix nano it is quite small. However 60 cm a year is perhaps ok ;))) – mplungjan Jun 07 '11 at 11:56
  • OED hasn't got it; but I immediately thought it in answer to the question, and would understand it if I encountered it. – Colin Fine Jun 07 '11 at 13:39
  • I agree with @Colin on this; it seems like the natural formation to use for this word. However, I suspect that lots of people won't understand it because they aren't familiar with "sesqui-" at all (and thus wouldn't understand sesquicentennial either). – Mr. Shiny and New 安宇 Jun 07 '11 at 14:25
  • Can this word also be used for "takes/took 18 months"? Such as "She just ruined her sesquiennial marriage"? – Felix Dombek Jun 07 '11 at 21:59
  • @planetjones the Plain English Campaign would probably have a thing or two to say about this: http://www.plainenglish.co.uk/ – Rei Miyasaka Jun 08 '11 at 07:35
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    @Rei Miyasaka I'm not sure sesquiennial is a clear example of the "gobbledygook, jargon and misleading public information" which the plain English campaign states they are against. – planetjones Jun 08 '11 at 08:50
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    @Felix Dombek: no, something that has been around for 18 months is not the same as something that happens every 18 months. – Matt E. Эллен Jun 08 '11 at 14:54
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    @planetjones If you need to look up a dictionary to understand a word that might be used in a legal document when it could otherwise be described by a phrase of common words, then it might as well be. – Rei Miyasaka Jun 08 '11 at 20:15
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I think JoseK's answer is the correct one, but there are also a few google hits for 'semi-triannual' and even a few for the (more correct, because unambiguous) 'semi-triennial.' Either of these might be easier for casual readers to decipher than 'sesquiennial,' since 'semi-' and 'tri-' are more familiar than 'sesqui-'.

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senderle
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    The root is not "sesqui-" but "se" (which comes from semi-). "qui" is a "conjuction". – Alenanno Jun 07 '11 at 14:54
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    @Alenanno, I'm not talking about roots, I'm talking about English-language prefixes. 'sesqui-' may not be a single root, but it is a single prefix; it's in the dictionary. – senderle Jun 07 '11 at 15:47
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    I was talking about the original term. :) – Alenanno Jun 07 '11 at 15:50
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    +1 not because it's the 'right' answer, but because semi-triennial is potentially more comprehensible to millions of people on first encounter than sesquiennial. I find it somewhat ironic that @Josek's only quoted usage example feels the need to define the term immediately after writing it! :-) – FumbleFingers Jun 07 '11 at 17:24