Webster's Revised Unabridged Dictionary · 1913

Biennial

Biennial ({not transcribed}) , adjective

[Latin biennalis and biennis, from biennium a space of two years; bis twice + annus year. Compare Annual.]

1.
Happening, or taking place, once in two years; as, a biennial election.
2.
(Botany) Continuing for two years, and then perishing, as plants which form roots and leaves the first year, and produce fruit the second.

Biennial , noun

1.
Something which takes place or appears once in two years; esp. a biennial examination.
2.
(Botany) A plant which exists or lasts for two years.