The two words biannual and biennial are easily confused.

Both come from Latin bi-, twice, and annus, year.

Biannual means occurring twice a year, and biennial means occurring every second year – think of the Venice Biennial (in Italian la Biennale di Venezia).

Perhaps you polish your car or clear out your garage twice every year – then that is a biannual activity. If you go to a conference that is held every two years, you attend a biennial conference.

Biennial can also refer to a plant that blooms or bears fruit in its second year and then dies.

Instead of biannual, you can write semiannual; both words refer to something happening twice a year or every half year.

Biweekly and bimonthly don’t have this distinction – there is no vowel as in annus that could show the difference. Biweekly could mean both twice a week and once every second week. A bimonthly magazine could be one that is published twice a month or every two months. As a writer, you need to make it clear what you intend to say.

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