I organize an event once every two months:
January 5th, March 5th, May 5th, etc.

I want to convey that frequency to an international audience.
Is there any unambiguous adjective for this?

I would say "It is a bi-monthly event" but I am afraid by the fact that is also seems to mean "twice a month". Is there anything better?

  • There would never have been this problem if people used "fortnightly" or "fortnight" (mutter... mutter). Use the expression bimonthly, people will read further and understand that the events occur every two months.
    – Mari-Lou A
    Jan 15, 2015 at 7:46
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    Isn't "fortnightly" every two weeks? And thus not a suitable replacement for the twice-a-month sense of bi-monthly? Jan 15, 2015 at 9:47
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    @BrianHitchcock I think the meaning is that if people only used fortnightly and never bimonthly there wouldn't be a problem. Strictly fortnightly is not the same as semi-monthly, but anyway if wishes were horses, etc.
    – Jon Hanna
    Jan 15, 2015 at 14:29
  • @jon hanna Yes, that's exactly what I meant. The adjectival term for every two weeks is "fortnightly", if people used that instead of "bimonthly", there would be no ambiguity. Do people think "biennial" means twice a year?
    – Mari-Lou A
    Jan 15, 2015 at 15:16
  • @Mari-LouA no, but biannual has the same problem. Biennial is more comparable to bimestrial both in meaning and origin.
    – Jon Hanna
    Jan 15, 2015 at 15:35

3 Answers 3


An alternative expression ( though less common) is bimestrial: (TFD)

  • Occurring every two months; bimonthly.
  • @JonHanna: I get paid fortnightly. So I get 26 paychecks a year. Someone who gets paid bi-monthly gets 24 paychecks a year. This is a significant difference, especially when it comes to paying the rent on the 1st of the month. So why don't we just say "semi-monthly" rather than wishing for horses? Jan 16, 2015 at 7:14

Your best option is probably "every two months", unless something else would make it clear that bimonthly was not used in the sense synonymous with semi-monthly.

Bimestrial has the meaning you want, but is obscure, while "every two months" is plain English and unambiguous.


Oxford dictionaries confirms that the meaning of 'bimonthly' is in fact ambiguous.

Unfortunately it means both! ... The same ambiguity affects biweekly and biyearly. If you want to be absolutely clear, it's best to use a phrase such as 'twice a week' or 'every two years'.

Your event occurs 'every two months.' There is the apparent downfall that not saying 'bimonthly' could give the sense of a limited vocabulary. If this is the concern, I would recommend stating that your event is "bimonthly (once every two months)." This is unambiguous and conveys both your knowledge of the appropriate term and your understanding that the term is ambiguous.

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    That has its own unfortunate pitfall, however: rather than giving off the impression that you have a limited vocabulary, you risk giving off the impression that the reader has limited vocabulary and needs long words explained. Jan 15, 2015 at 14:40

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