For me, the word "bimonthly" has always been confusing whether it means twice a month or once every two months. Looking up the word in some dictionaries today, I noticed that all the dictionaries I checked it up define the word as something like "every two months OR twice a month". Below are some examples.

Collins Dictionary https://www.collinsdictionary.com/
1. every two months
2. (often avoided because of confusion with sense 1) twice a month; semimonthly

Merriam-Webster https://www.merriam-webster.com/
1. occurring every two months
2. occurring twice a month : semimonthly

Oxford Learner's Dictionaries https://www.oxfordlearnersdictionaries.com/
produced or happening every two months or twice each month

Longman Dictionary https://www.ldoceonline.com/
appearing or happening every two months or twice each month

Since the "every two months" definition always comes first in all those dictionaries, I assume that it is the commonly-understood meaning by native speakers in general, but how can you be so certain that it really means every two months?

  • 2
    If the dictionaries can't agree on a definition, then what chance do we stand?
    – BillJ
    Jul 29 '20 at 10:52
  • 3
    I personally never use any of the bi-[time period] words, simply because they are so ambiguous. If I mean twice a month, I say twice a month; if I mean every other month, I say every other month. There is no reason to use a single word that's ambiguous over three words that are completely unambiguous. Jul 29 '20 at 15:03
  • I agree with Jason. The problem is how to interpret the word when it is written. Can I just assume that in nine out of ten cases it means every two months?
    – Takashi
    Jul 29 '20 at 22:37
  • @Takashi its probably more like 60/40 in favour of 'every two <whatever>' Jul 31 '20 at 9:58
  • 1
    Does this answer your question? Bi-Monthly (once every two months)
    – ColleenV
    May 25 at 14:04

Those definitions are correct, bi-monthly (or indeed bi-weekly, bi-yearly etc.) is ambiguous. The fact that it is still commonly used is basically inexplicable. Sorry!

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