The terms “biweekly” and “bimonthly” continue to generate confusion due to their inherently ambiguous meanings, according to linguistic resources and historical usage. While dictionaries such as Merriam-Webster and Cambridge acknowledge that “biweekly” can mean either “every two weeks” or “twice a week” and that “bimonthly” might signify “every two months” or “twice a month,” this dual interpretation often leads to misunderstanding.

The ambiguity of these terms is well-documented, with examples tracing back to the 19th century. In 1884, The Microscopical Bulletin and Optician’s Circular highlighted reader confusion when subscribers missed issues, noting that “bimonthly” was commonly—but not consistently—understood to mean “twice a month.” The British lexicographer Ebenezer Cobham Brewer described the situation as “quite indefensible” in 1877 and criticized the mixture of Latin prefixes with Germanic roots, suggesting alternatives like “twyweekly” for clarity. Despite such historical objections, these terms have persisted in modern usage.

Standard style guides, including The Associated Press and The Chicago Manual of Style, generally define “biweekly” as occurring every two weeks and “bimonthly” as every two months. However, the widespread acceptance of the alternative meanings requires dictionaries to acknowledge both interpretations, perpetuating the challenge in everyday communication.

Adding to the complexity, the prefix “bi-” behaves differently when applied to other time-related terms: “biannual” denotes twice a year, whereas “biennial” means once every two years. This inconsistent pattern does little to resolve the confusion around “biweekly” and “bimonthly.”

Experts suggest various approaches to mitigate uncertainty. Some recommend using “semimonthly” for “twice a month,” though that label itself is not universally understood. Linguist Michael Adams has proposed reviving “fortnight” to denote a two-week period, which would avoid ambiguous usage, though a fortnight is not identical to half a month, leading to discrepancies in frequency counts, such as paycheck schedules.

The prevailing advice from language commentators is to avoid “biweekly” and “bimonthly” altogether when precision is necessary. Instead, it is recommended to use clear, explicit phrases like “twice a month” or “every other month” to ensure clear communication.

Despite efforts to regulate usage and encourage clarity, the persistent ambiguity of “biweekly” and “bimonthly” reflects broader challenges in language evolution, where words may carry different meanings depending on context and speaker intent. This ongoing issue underscores the difficulty in achieving absolute precision in everyday language.