bi ‧ en ‧ ni ‧ al /baɪˈeniəl/ BrE AmE adjective
[ Date: 1600-1700 ; Language: Latin ; Origin: biennium 'two-year period' , from bi- ( ⇨ ↑ bi- ) + annus 'year' ]
1 . a biennial event happens once every two years ⇨ annual
2 . a biennial plant stays alive for two years
⇨ annual
, perennial
—biennially adverb