A Word, Please: Does bimonthly mean twice a month or every two months? The answer depends

Do you get paid bimonthly or biweekly? It may be both, writes grammar columnist June Casagrande.
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Not long ago I would hear people talk about getting paid bimonthly. Others, workers who got paid on a very similar schedule, talked about getting paid biweekly.

Sometimes in February, they all got paid on the same days. The rest of the time they got paid at nearly identical intervals, about 14 or 15 days between paychecks.

We can reasonably assume that some of them subscribed to magazines that arrived every 60 days or so. Chances are they referred to these publications as “bimonthly.”

Fascinatingly, it seems no one got confused by these two different meanings of the prefix “bi-.” When a worker who got paid every 15 days said he was paid bimonthly, everyone knew what he meant.

And when the same worker said his magazine that arrived six times a year was “bimonthly,” everyone knew what he meant.

So what does “bi-” mean? Does it mean two times per, as in two times per month, or does it mean every two, as in every two weeks?

The answer: both.

Here’s one definition for the prefix “bi-” from Merriam-Webster’s Collegiate Dictionary: “occurring every two: bicentennial.” Here’s another definition in the same dictionary: “coming or occurring two times: biannual.”

So even though biweekly is universally understood to mean every two weeks, bimonthly can mean every two months or twice a month. Context counts, as is noted by Merriam-Webster’s Dictionary of English Usage (which unlike Merriam-Webster’s Collegiate is not a dictionary but a usage guide).

“In the publishing world,” reports the usage guide, “everyone assumes you know ‘bimonthly’ means every two months. … On the other hand, we have evidence that in the world of education, ‘bimonthly’ usually means ‘twice a month.’”

Merriam’s usage guide cites a number of sources, like a magazine called Scouting that in 1970 informed readers ”There will now be 6 issues a year. Each bimonthly issue will have 48 pages.”

Another example offered in the usage guide is from the 1971 novel “The Paper Chase”: “None of us have time to meet twice a week. … I propose we shift to bi-monthly meetings.”

In all, Merriam’s includes five examples in its discussion of the prefix “bi-” and they all have something in common. They’re all from the 1960s or 1970s.

This reinforces the idea I hinted at when I started this column talking about at time “not long ago.” Confusing uses of “bi-” seem to be on the decline.

I checked Google Ngram Viewer — a searchable database of books going back centuries. Lo and behold: Ngram Viewer’s chart shows a precipitous decline in the use of the word “bimonthly” starting in the late 1980s.

Occurrences of “biweekly” have also dropped significantly since the ’80s, but not nearly as much as “bimonthly.”

Ngram Viewer doesn’t tell us everything we might want to know about “biweekly” and “bimonthly.” But it’s interesting.

People who worry too much about the degradation of the English language can take heart in this tale of “bi-.” It’s astounding how little confusion this prefix has caused.

Meanwhile Americans are abandoning its more confusing uses. It shows that the English language is pretty good at policing itself.

Of course, the prefix “bi-” still carries some danger you’ll confuse your reader. But with a little vigilance you can sidestep the pitfalls.

In Associate Press editing style, for example, editors are instructed: “Biweekly means every other week. Semiweekly means twice a week.” Good advice easily applied to “bimonthly.”

The Chicago Manual of Style has good tips, too. “Generally, bi- means two (biweekly means every two weeks), while semi- means half (semiweekly means twice a week). Because these prefixes are often confused with each other, writers should be explicit about the meaning.”

With a little care, you can use “bi-” with no risk of creating confusion. In fact, you probably already do.

June Casagrande is the author of “The Joy of Syntax: A Simple Guide to All the Grammar You Know You Should Know.” She can be reached at