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
    Commented Jul 29, 2020 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. Commented Jul 29, 2020 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
    Commented Jul 29, 2020 at 22:37
  • @Takashi its probably more like 60/40 in favour of 'every two <whatever>'
    – MikeB
    Commented Jul 31, 2020 at 9:58
  • 1
    Does this answer your question? Bi-Monthly (once every two months)
    – ColleenV
    Commented May 25, 2021 at 14:04

1 Answer 1


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!

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .