\Bi*en"ni*al\, a. [L. biennalis and biennis, fr.
biennium a space of two years; bis twice + annus year. Cf.
{Annual}.]
1. Happening, or taking place, once in two years; as, a
   biennial election.
2. (Bot.) Continuing for two years, and then perishing, as
   plants which form roots and leaves the first year, and
   produce fruit the second.

\Bi*en"ni*al\, n.
1. Something which takes place or appears once in two years;
   esp. a biennial examination.
2. (Bot.) A plant which exists or lasts for two years.