What’s the difference between biweekly and semiweekly or bimonthly and semimonthly?
Since biweekly can also mean semiweekly, you might wish to be clearer and use terms like every two weeks instead of biweekly.
USAGE: The meaning of bimonthly (and other similar words such as biweekly and biyearly) is ambiguous. The only way to avoid this ambiguity is to use alternative expressions like every two months and twice a month. In the publishing world, the meaning of bimonthly is more fixed and is invariably used to mean ‘every two months.’ (Source: The New Oxford American Dictionary)
The rule is different when we use the word annual.
USAGE: Biennial means ‘lasting or occurring every two years’: Example: Congressional elections are a biennial phenomenon. A biennial plant is one that lives a two-year cycle, flowering and producing seed in the second year. Biannual means ‘twice a year’: The solstice is a biannual event. (Source: The New Oxford American Dictionary)
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