Pronunciation: (bī-en'ē-ul),[key] —adj. 1. happening every two years: biennial games. 2. lasting or enduring for two years: a biennial life cycle. 3. Bot.completing its normal term of life in two years, flowering and fruiting the second year, as beets or winter wheat.
—n. 1. any event occurring once in two years.
2. Bot.a biennial plant. Also,biyearly(for defs. 1, 2).