noun a plant which exists or lasts for two years.
2. biennial ·adj happening, or taking place, once in two years; as, a biennial election.
3. biennial ·noun something which takes place or appears once in two years; ·esp. a biennial examination.
4. biennial ·adj continuing for two years, and then perishing, as plants which form roots and leaves the first year, and produce fruit the second.