Given that tri-hourly means thrice every hour, how then do I say every three hours?

  • 2
    Could you please explain why you think you need this? How would you use it in a sentence?
    – tchrist
    Aug 23, 2014 at 16:05
  • 2
    According to this authority it is not even clear whether bi-weekly means once every two weeks, or twice a week. Similarly with bi-monthly. Apparently they can mean either. So before we get on to three, perhaps we should get two sorted out! data.grammarbook.com/blog/definitions/…
    – WS2
    Aug 23, 2014 at 21:05
  • Medical prescriptions may use the abbreviation q.3 h or q.3° which is short for quaque 3 hora. 3 may be switched out with other numbers.
    – jxh
    Aug 24, 2014 at 19:05
  • 1
    I have never heard the expression "tri-hourly" and I would never remember whether it means "three times every hour" or "once every three hours". Best to say it the long way, especially if the timing is critical, as it would be for medicine or checking a nuclear reactor. Nov 25, 2020 at 17:08

3 Answers 3


This kind of questions can have two possible answers.

  1. We half-resurrect, half-invent an obscure half-Greek, half-Latin word that nobody ever uses or understands. Then as soon as you need to say "every 48 hours", or "every 113 weeks", you have to ask the exact same question all over again, because you have no idea what the Latin for "48" is, or the Greek for "week".

  2. We encourage you to not reinvent the wheel and just go with "every three hours". You used these exact words to explain the concept to us, so there's nothing stopping you from using these exact words to explain the concept to others. The construction is perfectly natural, ubiquitous, universally understood and extremely productive to boot. You can just say "every" followed by any number followed by any unit, and you're done. Doesn't have to be time units, even. Can be miles, liters, degrees, Joules, leaves, houses or ticks. Which is sort of the whole point of languages: not to come up with a dedicated word for absolutely everything, but to have a bunch of very simple words that can be combined in very simple ways to form very complex thoughts.

To me, it is a no-brainer that answer (2) is vastly superior. And so it's also the one I'm going with here.

  • 5
    +1 Can this become an automatic Javascript tooltip thing for people asking for single words?
    – user85526
    Aug 23, 2014 at 17:25
  • It just applies to like every question asked under this tag.
    – user85526
    Aug 23, 2014 at 17:26
  • -1 Or you just use trihoral in this case.
    – Frank
    Aug 23, 2014 at 17:48
  • 3
    @Frank: as I said, please do go on to provide the corresponding words for every 11 hours, 38 hours, 113 hours, 15227 hours. The OP has a nice fish, but doesn't know how to get more. And he must be aware just how many readers will have to look it up. People who don't know trihoral will have to look it up, and even people who do know it might need to check if it really means what they think it means and isn't the same thing as trihourly. And even after all that, the readers still can't be sure if the author is not confusing the two, failing to express the intended meaning.
    – RegDwigнt
    Aug 23, 2014 at 18:26
  • 2
    @Mitch until your boss walks in and says, that script you've been running every 113 hours, we've had a board meeting and a focus group, and now you must run it every 15227 hours instead. He will do just that. That's an essential part of his job description.
    – RegDwigнt
    Aug 23, 2014 at 19:35

I have seen this:


adj. Occurring once in every three hours.




but I leave the word to native speakers on the matter.

  • So trihoral is every three hours in the same way fortnightly is every fourteen nights. Perfect.
    – Frank
    Aug 23, 2014 at 17:01
  • 1
    It's kind of funny because in my native language we call it "pompino" :-)
    – Pam
    Aug 23, 2014 at 17:35
  • 2
    I'll believe that 'trihoral' means 'every three hours' but I don't think that many native speakers would recognise it. This native speaker certainly didn't.
    – BoldBen
    Nov 25, 2020 at 17:01
  • @BoldBen - Me neither. No matter how many times I read it, I would not remember whether it meant "3 times per hour" or "once every three hours". Nov 25, 2020 at 17:19

As a hint in such cases, better stick to the (even old-?) English roots or other Germanic roots when in doubt about which word fits better.

"tri-hourly" is showing this at its best, neighboured to "tri" like in Triathlon is "bi" like in Biathlon:

  • "bi-hourly", like "bi-monthly" likely already from the 1800s and perhaps even before, can nowadays mean both "every two hours" and "twice per hour"!
  • and "semi-hourly" did not make it clearer but was misunderstood again after some time.

Taken from bimonthly.

This shows best that Greek/Latin rooted English words are often misunderstood over time. This blurs not only the roots of English but also the loan word itself in the end. Thus, if already the neighboured "bi-hourly" is mixed up, do not use "tri-hourly" either.

In German, it is like:

  • 3x/h: "[three times hourly]", "[three times each hour]", while the most often "[three times per hour]" has Latin roots and should not be taken when following old roots here;
  • 1x/3h: "[every three hours]", "[three-hourly]", "[each third hour]";

while "[every third hour]" is wrong in German.

"[]" = to be read as if it was German, this is not meant to be English!

Again, if you want to find out what could be right, take the neighboured "other" in German.

English has this nice thing in the middle: "every other week" with "other" meaning a kind of "next" or "on the other side" so that you do not need to say "each other week" :). In German, it would be wrong to say "[every other week]", and "each other week" does not say "second".

By the way, "second" is also Latin. English has just lost its "twey" for German "zwei", Dutch "twee" and does not make it "twey-th" for German "zwei-te", Dutch "tweede" to make it an 'English' "second", and "two-th" would sound like "tooth" :) while other Germanic branches can change from the -o to -e to get this done.

This "other" for "second" (brrrr) can also be found in other Germanic roots. It is very rare and happens almost never, but you could say both "[each other week]" and "[every other weeks(!)]" even sometimes in German when you want to say that of a choice of weeks, you take "the other side that is not chosen". This can happen when you plan the cleaning of the house with two people and one has already taken all of the even weeks. But it is not used as the normal "[second]" in German as "other week"="second week" is in English.

Unlike in English with its "each other", the German "[each other week]" does not stand against the German "each other", since there is no such "[each other]". In German, you do not have "each other" but "[against-sidely]" and "[each's-sidely]" and "[all's-sidely]" which all have slightly other meanings :).

What is this all about? It is to show how to catch the right feeling of long forgotten roots. There is often a hidden rule that can be found. The rule here is to better drop anything that is wrong in another Germanic language. Thus, do not say "every other week" or "every second week". It goes without saying that this is also meant for "every third week". Even if it is right in nowadays English, it is wrong in German, and English was perhaps just blurred by centuries on that far foggy island outside in the waves :). Latin or Greek rooted words only make it worse. As in the other answer here, take "every three hours" and "three times per hour" and it would be right in German as well.

Needless to say: week, month, day, hour and so on are treated the same.

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