Biennially

happening every two years:
biennial games.
lasting or enduring for two years:
a biennial life cycle.
Botany. completing its normal term of life in two years, flowering and fruiting the second year, as beets or winter wheat.
any event occurring once in two years.
Botany. a biennial plant.
Historical Examples

The Armies of Labor Samuel P. Orth
Alden’s Handy Atlas of the World John B. Alden
The South-West Jonathon Holt Ingraham
Trees and Shrubs for English Gardens Ernest Thomas Cook
Martin Van Buren Edward M. Shepard
Trees and Shrubs for English Gardens Ernest Thomas Cook
Publications of the Mississippi Historical Society, Volume 2 (of 14), 1899 Various
Constitution of the State of North Carolina and Copy of the Act of the General Assembly Entitled An Act to Amend the Constitution of the State of North Carolina North Carolina
Why We Punctuate William Livingston Klein
Elements of Civil Government Alexander L. Peterman

adjective
occurring every two years
lasting two years Compare biannual
noun
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)
an event that takes place every two years
adj.
biennial
(bī-ěn’ē-əl)
Adjective Completing a life cycle normally in two growing seasons.

Noun A biennial plant. In the first year, biennials normally produce a short stem, a rosette of leaves, and a fleshy root that acts as food supply. In the second season, biennials blossom, produce seed, use up their food supply, and die. Carrots, parsnips, and sugar beets are examples of biennials. Compare annual, perennial.