How often is “bimonthly”?

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If something is “bimonthly”, does it occur twice a month or once every two months? In fact, just to demonstrate how slippery the English language can sometimes be, the correct answer would be “either”. The Oxford English Dictionary definition is very straightforward : 

appearing or taking place twice a month or every two months.”

It’s fair to say that “every two months” would be the more common usage of the word, but there’s no guarantee that a reader will assume one meaning or the other. If you want to use the term it may be worth spelling out (at least once) what you mean by it. Or just use different words, such as “every two months”. In the US, the word “semimonthly” is often used to mean “twice a month” but this is not a common word in other parts of the world, such as the UK. 

The same problem occurs with words for other periods of time. Bi-weekly, for example, can mean both “twice a week” and “once every two weeks”. So, strictly speaking it isn’t clear whether a “bi-weekly” publication will appear once or four times over a two week period.

Similarly a biannual magazine could be published once every six months or once every twenty-four. On the other hand, the word “biennial” is unambiguous and means “once every two years” or “lasting two years”. This word is thus often used to refer to plants that only flower or fruit in their second year of life. 

The ambiguity of language can be a part of its beauty, especially if you are writing fiction or poetry. But if you want to be sure of conveying a precise meaning, there are some words that are best avoided. 

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17 thoughts on “How often is “bimonthly”?”

  1. As a speaker or writer, it’s easy and sensible to avoid “bimonthly” and use either “fortnightly” or “every two months”, but that doesn’t solve the problem of guessing what someone else meant when they use it.

    Similarly, although there is a difference between “biannual” (twice a year) and “biennial” (every two years), I suspect many are unaware of that distinction, so both are best avoided.

  2. Thank you for this post. I frequently have to ask people what they mean when they use these “bi” terms.

    I wonder, though, where you got the information that “every two months” would be the more common usage of bimonthly. I worked for a multinational corporation with hundreds of thousands of employees. We were paid bimonthly–which was every 2 weeks. “Bimonthly” was frequently used in this corporation, and always meant every 2 weeks to everyone.

    I agree, the terms are very ambiguous.

  3. Twice a — works well for me. Cuts the confusion. Fortnight is UK to me (I’m USA), but easier to understand than bi–. Would rather plain and simple than have to guess at what the writer is meaning. Glad I’m not alone in the confusion.

  4. “Sennight” is a lovely word – it just means one week (from “seven nights, just as fortnight is from “fourteen nights”) – but it is considered archaic these days, unfortunately.

  5. I completely agree on the fact of how the English language can be so slippery and misused. When using the English language, sometimes it can become very tricky depending on the origins. Dutch including other languages has contributed to the English slang but that does not mean its a bad thing. Bimonthly can be used as an adjective, adverb and noun so that may confuse people into using it in the wrong manner. I say in order to be safe when using words that you are not too sure about, Just don’t use them at all unless you do a little background check. Great blog! I look forward to reading more of your blog posts.

  6. @Taja: Bimonthly as a noun? I beg to differ.

    The problem with bimonthly isn’t what sort of word it is, but rather, what it means. Best to avoid it.

  7. what does bisect mean?.. Cut in two.. I’m really amazed that the dictionary has two meanings that are vastly different. Pick one, publish it and be done. Biannual, means twice a year. Bilateral contract means two parties, not two contracts. Bisexual, favors both sexes in one person… not favors two partners.
    Biweekly, twice a week
    Bimonthly, twice a month
    Biannual, twice a year.
    Quarterly, 4 times a year, every three months
    fortnightly, every two weeks.. (note: not the same as bimonthly as there are more than 4 weeks in some months..)

  8. Alex, a dictionary that did that wouldn’t be very useful, for two reasons:

    1. Most people never look at a dictionary at all, let alone for words they think they know the meaning of and can spell, so they would never discover the new/only meaning.

    2. Because of the above, some people would still use the words in the “wrong” way and anyone who did look in a dictionary for clarification would see only one meaning and assume that was the one that was meant, even though it wasn’t.

  9. this blog is really really great; first of all, i have never heard or come across the word sen-night or forthnigth but today, i got to know about it through this blog. so who ever started this is truly doing a great job…..

    but one more thing, if twice in a months is called bimonthly what then will once in two months be called

  10. @Cecily- 1) Very true, however, there would be a place to point them toward. 2) We’d need to make a new word for “Every Two Months”…..

    OR, I actually took 10 min time to reflect on the above.
    bi- from my latin class means two. so…bisect really means two sections not cut in two. Bipedal, like us humans means two feet. Semi means “in two.” Take this route and you have my list above but modified… and I do think this will fix everything.
    SemiWeekly, twice a week
    Biweekly, every other week, same as fortnightly
    SemiMonthly, twice a month, say 1st and 15th
    Bimonthly, Every other Month
    Biennial, twice a year
    Quarterly, 4 times a year, every three months
    Annually, yearly
    Biannually, every other year

    So, I switched teams and will begin using the above in my meeting notices. With the above explaination to back me up.

  11. Thank You Alex… You said it succinctly. The Publishing Bus. at some point in time made up their own meaning. I’ll continue to use it that way & be wrongly corrected by those of limited experience.

  12. Alex, “biennial” is the one “bi-” word indicating a period of time about which there is no dispute: It means once in or every two years and in particular has been used as such in the world of horticulture for plants that flower every second year. In your proposed scheme, it is “bi-annual” that would have to mean twice a year.

  13. “Bi-sect” – describes the action of taking a whole, cutting (sect) it in two (bi-) to obtain two bits, which could be uneven, but in the absence of description to the contrary, let’s assume two halves.

    Bi-annual – describing something that occurs in two parts of the year ie twice a year, usually but not necessarily every six months. “Six-monthly” where it is precisely that, “bi-annual” where it could be unevenly spread across the twelve months.

    Ditto, therefore, for bi-monthly (= twice in one month) and bi-weekly (twice in one week).

    Fortnightly (uncontentiously) means every two weeks or once in two weeks (and sennight, apparently – thanks for that contribution, Peter – means weekly or once a week).

    The need, if there is one, if for a snappier way of saying every two months in the same way that we have “quarterly” for every three months. Quarterly derives from “quarter-yearly” and equates to half-yearly, which is synonymous with bi-annually. The richness of English allows synonyms to convey nuanced as well as sharply distinct meanings. It would be usual for a company to release half-yearly earnings figures, rather than bi-annual figures, although the half-yearly results would be released bi-annually (if you’ll excuse the tautology). A word is needed for the division of a year that is a two month period – ie a sixth part. Failing that, we are left with describing two months as a multiple of one month – ie two-monthly, every two months, once in two months. That the English did not come up with a word for two months perhaps reflects that such a period of time was of no use to them in their lives. Seasons are quarterly, the legal calendar is quarterly (“Quarter Sessions”), financial reporting is quarterly. All that said, I recall having used “bi-monthly” to mean two months without having checked or thought about it, but realising now that it seems illogical to do so.

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