/ baɪˈeniəl; NAmE / adjective , noun
■ adjective
[ usually before noun ] happening once every two years :
a biennial convention
► bi·en·ni·al·ly adverb
—see also annual , biannual
■ noun
any plant that lives for two years, producing flowers in the second year
—compare annual , perennial
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WORD ORIGIN
early 17th cent.: from Latin biennis (from bi- twice + annus year) + -al .