We don't have synonyms for biennials yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are biennial, biennale and biennially.
(n) :
A plant that requires two years to complete its life-cycle, germinating and growing in its first year, then producing its flowers and fruit in its second year, after which it usually dies.
(n) :
A plant that requires two years to complete its life-cycle, germinating and growing in its first year, then producing its flowers and fruit in its second year, after which it usually dies.