Does “bimonthly” mean twice a month, or every other month?

Bi- can be a confusing prefix when used with units of time. You’re an educated audience, so I’m sure you know that bisect means to cut something in half. But in the case of bimonthly, and its sibling, biweekly, it isn’t clear that it means to “cut the time in half”. Lexicologists (people who study words) tell us that in publishing, bimonthly means “every two months.” A bimonthly publication is one that comes out six times a year. In other fields, however, it means twice a month.

Things are complicated by the words biannual and biennial. The first means “twice a year,” and the second, “every two years,” but people tend to mix them up as well.

What to do?

Many have decided to use the prefix semi- in those cases when they mean twice a week, month, or year. This works when you have bi- and semi- near each other, so the contrast becomes clear. “We will begin to hold staff meetings semi-monthly, rather than the current bi-weekly schedule.” But it’s not the best solution, because it doesn’t offer readers any clues as to what bi- means when it’s in isolation.

It may be best, because the confusion is so widespread, to say explicitly what you mean; for example, “twice a month,” or “every other month.” Leave no room for confusion.

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2 Responses to Does “bimonthly” mean twice a month, or every other month?

  1. Lars Walker says:

    You’ve set my mind at ease. I thought I was the only one who was confused about this.

  2. JP says:

    Another option to semi-monthly is "twice-monthly". I think that works better. "We will hold meetings twice-monthly".

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