ETYM Latin biennalis and biennis, from biennium a space of two years; bis twice + annus year. Related to Annual.
1. Occurring every second year; SYN. biyearly.
2. (Botany) Having a life cycle lasting two seasons; SYN. two-year.

A plant having a life cycle that normally takes two seasons from germination to death to complete; flowering biennials usually bloom and fruit in the second season.
A plant living for two years and flowering in the second.