Usage of Bimonthly
Bimonthly and biweekly are inherently ambiguous because bi- can mean both "occurring every two" and "occurring two times." This ambiguity cannot be eliminated by the dictionary. If you need bimonthly or biweekly, we suggest leaving some clues in your context about which sense of bi- you intend. Note that if you need the meaning "twice a," you can also substitute semi- for bi- without additional clarification: semimonthly, semiweekly. Dealing with years is generally simpler: biannual usually means "occurring twice a year" and biennial usually means "occurring every two years."
Did you know?
When we describe something as biannual, we can mean either that it occurs twice a year or that it occurs once every two years. So how does someone know which particular meaning we have in mind? Well, unless we provide them with a contextual clue, they don’t. Some people prefer to use semiannual to refer to something that occurs twice a year, reserving biannual for things that occur once every two years. This practice is hardly universal among English speakers, however, and biannual remains a potentially ambiguous word. Fortunately, English also provides us with biennial, a word that specifically refers to something that occurs every two years or that lasts or continues for two years.
Cite this Entry
“Biannual.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/biannual. Accessed 14 Oct. 2026.
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