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'Biannual' occurs twice a year; 'biennial' occurs once every two years.
Side-by-side comparison
"Biannual" means twice a year. It is ambiguous because some people confuse it with "biennial". If you need to be precise, say "twice a year".
The biannual performance review takes place every June and December.
The magazine moved from monthly to biannual publication to reduce production costs.
Biannual dental check-ups are recommended for maintaining good oral health.
"Biennial" means every two years. It can also be a noun referring to plants that live two years or to events that take place every other year.
The Venice Art Biennale is one of the most prestigious biennial events in the art world.
The committee holds a biennial conference alternating between London and New York.
The plant produces flowers only in its second year, making it a biennial species.
Common mistake
Even native speakers mix them up, since the two words differ by just a few letters. That is why in a contract or a calendar the safest move is to write out the full phrase instead of the adjective.
Trick to remember it
- •"Biannual" contains "annual": BI + ANNUAL = twice within the same year.
- •"Biennial" comes from Latin "biennium" (two-year period): once within that period.
Quick rule
- •"Biannual" = twice a year.
- •"Biennial" = once every two years.
- •When in doubt, write "twice a year" or "every two years".
Did you know?
The Venice Biennale (1895) gave "biennial" its prestige in the art world, alternating yearly between visual art, architecture, cinema, and other forms. The Latin prefix BI- is genuinely ambiguous: "two per unit" or "one per two units". To eliminate the confusion, many organisations prefer "semi-annual" (twice a year) over "biannual". In botany, "biennial" has a precise technical meaning: plants that require two growing seasons to complete their life cycle, such as carrots, parsley, and beets, which only flower and seed in their second year.
Practise what you learned
Exercise 1 · Pick the right one
The festival only happens every two years. It's a _____ event.
Exercise 2 · Pick the right one
The magazine is published twice a year. It's _____ .
Exercise 3 · Form the word
Related word pairs
One means to receive or agree to something, the other means to exclude or not include.
'Advice' is the guidance you receive (noun); 'advise' is the act of giving that guidance (verb).
'Affect' is the verb meaning to influence something; 'effect' is the noun meaning result or consequence.
'Aisle' is the walkway between rows of seats or shelves; 'isle' is a small island.
Bryan López
Founder of SpeakUP Academy