What does bimonthly mean?
Bimonthly is an adjective and adverb describing something that happens either once every two months or twice a month — an ambiguity that has made it one of English's most famously confusing words. It derives from the prefix "bi-," meaning "two," combined with "monthly." In practice, many readers assume it means "every two months," following the pattern of bicentennial (every two hundred years), while others interpret it as "twice a month," parallel to semiannual-style usage. This split has persisted for well over a century, prompting dictionaries to list both meanings and style guides to advise against the word altogether in favor of explicit phrases like "every two months" or "twice a month." Bimonthly also functions as a noun for a publication issued at such intervals, though this use is now relatively rare. It appears most often in workplace and publishing contexts — bimonthly meetings, newsletters, pay periods, and magazines.
Occurring or appearing every two months, or (less commonly) twice a month.
"The board scheduled its bimonthly strategy review for the start of March."
When precision matters, specify "every two months" or "twice a month" explicitly instead of relying on this adjective.
Once every two months, or twice a month; in a bimonthly manner.
"The journal is published bimonthly, with six issues appearing each year."
A periodical published every two months (or twice a month).
"He has subscribed to the gardening bimonthly since the 1990s."
This noun sense is relatively formal and increasingly dated; speakers more often say "magazine" or name the specific publication.
Used when referring to multiple bimonthly publications.
"The library's periodicals room keeps all the bimonthlies on open shelves."
"Bimonthly" means both "twice a month" and "once every two months" — which is why style guides beg you to avoid it entirely.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of bimonthly
Bimonthly was formed in English by combining the Latin-derived prefix "bi-," meaning "two" or "twice," with the native word "monthly." It emerged in the nineteenth century as part of a family of "bi-" frequency words alongside biweekly, biannual, and biennial, all of which inherited the same ambiguity between "every two" and "twice per." The prefix "bi-" itself comes from Latin bis, meaning "twice." Its closest siblings are biweekly and semimonthly, the latter coined partly to disambiguate the confusion that bimonthly created.
Related word forms
How bimonthly is actually used
Because of its ambiguity, careful writers often replace bimonthly with an explicit phrase such as "every two months" or "twice a month." Some publishers adopt the convention that bi- prefixes mean "every two" (bimonthly = every two months) while semi- means "half of" (semimonthly = twice a month), but this convention is not universal. The noun sense, meaning a periodical issued bimonthly, is somewhat formal or dated.
Easily confused with bimonthly
Semimonthly unambiguously means twice a month, whereas bimonthly can mean either twice a month or once every two months.
Biweekly follows the same ambiguous pattern as bimonthly but refers to weeks — either every two weeks or twice a week.