Both! Bimonthly can refer to something happening “every two months” or “twice a month.” Yep, bimonthly has, fittingly enough, two meanings.
What does bi– mean?
The prefix bi- means “two,” from the Latin bis, “twice.” A bimonthly publication can come out two times a month (on the second and last Friday, for instance) or every two months (January, then March, then May, and so on).
Now, what if your boss schedules biweekly meetings with you? Does that mean they occur twice a week (Tuesday and Thursday, for instance) or that you meet one time every two weeks (the first and last Mondays of the month, say)? It could mean both!
Then there’s biannual. A biannual event could take place twice a year (June, then December, for example) or every other year (2019, 2021, etc.). Honestly, we don’t even know what time it is, anymore.
Is there a clearer way to indicate dates?
Enter semi–, a prefix meaning “half” (also from Latin). Semimonthly is generally taken as “twice a month,” as if it cuts the month in half. Semiweekly happens “twice a week.” Semiyearly or semiannual falls “twice a year.”
If these words don’t come quickly to mind, you can always just be specific: “I’m setting up meetings twice a week” or “Let’s meet every other week.”
Or, you can take a page from British English’s playbook and use fortnightly. A fortnight is a period of two weeks. Fun fact: The fort in fortnight has nothing to do with Fort McHenry or the pillow forts you built as a kid. The word is smushed down from the Middle English fourtennight, from Old English fēowertēne niht—the span of fourteen nights (days).
If all else fails, context, context, context! If you get a new job that pays biweekly, odds are—given how the world works and all—you get paid every other week. But hey, if you want to pay us twice a week, go ahead then!
While we’re on this note …