A biennial event happens or is done once every two years.
...the biennial Commonwealth conference.
2. countable noun
A biennial is a plant that lives for two years. It flowers, produces seed, and dies in its second year.
biennial in British English
(baɪˈɛnɪəl)
adjective
1.
occurring every two years
2.
lasting two years
Compare biannual
noun
3.
a plant, such as the carrot, that completes its life cycle within two years, developing vegetative storage parts during the first year and flowering and fruiting in its second year
Compare annual (sense 3), perennial (sense 3)
4.
an event that takes place every two years
Derived forms
biennially (biˈennially)
adverb
biennial in American English
(baɪˈɛniəl)
adjective
1.
happening every two years
2.
lasting or living two years
noun
3.
a biennial event or occurrence
4. Botany
a plant that lasts two years, usually producing flowers and seed the second year
Derived forms
biennially (biˈennially)
adverb
Word origin
< L biennium, period of two years < bi-, bi-1 + annus, year + -al
Examples of 'biennial' in a sentence
biennial
So it is fair that these competitions are biennial.
Times, Sunday Times (2009)
So far, a chance to make a ninth appearance in the biennial match is miles away.
Times, Sunday Times (2008)
They are mainly biennial, so plant two years running to keep an annual display going.
Times, Sunday Times (2012)
The final round of the third biennial competition kicked off with a programme that seems weak and unexciting compared to the last two prize bills.
Times, Sunday Times (2008)
A fabulous biennial plant growing up to 4m high.
Times, Sunday Times (2013)
These are biennial plants, which means they should flower in the second year thendie, so yours must be itching to get it over with.