Is there a fourth word in this series: weekly, biweekly, triweekly, ...?

If not, and I had to coin a word, then would "quadweekly", "quadriweekly", or some other word be more etymologically appropriate? For example, is there a similar series from which I could borrow the prefix for "four"?

UPDATE: "Monthly" isn't appropriate because one month is a few days more than four weeks.

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    I once worked in a company that handled computerised accounts/payroll for lots of others. We used to call the stuff based on "four-week accounting period" fwaply [reports, etc.], to distinguish them from reports/companies based on calendar month. Commented Feb 23, 2012 at 21:53
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    If you wanted to impress, you could always try 'quadrihebdomadal'. Commented Feb 23, 2012 at 22:04
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    I like the sound of "fwaply". I'm afraid other people will find it rather unobvious though ;-) Commented Feb 23, 2012 at 22:07
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    @FumbleFingers "fwaply" is a great term, even though it sounds like something out of the mouths of upper-class twits.
    – Gnawme
    Commented Feb 23, 2012 at 22:11
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    @MichaelLiu The words with bi- are not obvious/unambiguous either. Consider "bimonthly". It can mean both "once every two months" and "twice a month".
    – Alenanno
    Commented Feb 23, 2012 at 22:14

3 Answers 3


Per Google, bifortnightly and bi-fortnightly together have been used about 5000 times on the web, frequently as objects of ridicule rather than as serious terms for "four-week-ly", occasionally as examples of misunderstanding of whether bi is a multiplier or a divider.

Although the lunar cycle is often thought of as 28 days, lunarly doesn't actually work to indicate 28 days, because the moon's sidereal period is only 27.3 days.

Regarding quadweekly and quadriweekly, I like quatriweekly or quatri-weekly better. Quadroon and quadrant, for example, use quadr- as one-fourth, while quatrain uses quatr- as four; but the roots of all of them are closely related to words meaning four.

  • Quatriweekly doesn't work, since quatrain came to English via French but we don't normally use it for our prefixes.
    – lly
    Commented Mar 31, 2017 at 11:06

Is there a compelling reason you cannot use "every four weeks"? The advantage of using the phrase is that there is less possibility of being misunderstood.

EDIT: You could also word it as "four-week" in the context you give in your comment below.

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    I have the phrases "weekly recurrence", "biweekly recurrence", "monthly recurrence", "annual recurrence", etc. For consistency, I'm looking for "(adjective) recurrence" for the four-week case. Commented Feb 23, 2012 at 22:15
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    If you coin a new word, it's possible you might confuse, annoy, amuse, or confound users. If you use something like "four-week recurrence" then you will improve usability, while sacrificing only a little consistency. Commented Feb 23, 2012 at 22:49
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    @MichaelLiu As further evidence of its naturalness, I submit the fact that you yourself used "four-week" as an adjective in your comment :) Commented Feb 24, 2012 at 2:26
  • Shakespeare, Roald Dahl and Dr. Suess called me and told me it's ok for folks to invent a new word now and then.
    – Kirby
    Commented Sep 7, 2022 at 18:02

There's nothing that's actually better than "every four weeks" unless this distinction comes up so much that your office creates their own jargon for it. (See above for the lovely fwaply.)

The problem with trying to sound clever by coining something from roots and prefixes is that the people who grok quadriweekly or quadweekly quickly and intuitively will also understand it's kinda off, since week is Germanic.

The best you've got is four-weekly unless you're showing off with tetrahebdomadally, quadriseptimanally, or duodetrigintally.

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