Happening, or taking place, once in two years; as, a biennial election.
- Lasting or living for two years.
- Happening every second year.
- Botany Having a life cycle that normally takes two growing seasons to complete.
- An event that occurs every two years.
- Botany A plant that normally requires two seasons to complete its life cycle, growing usually as a rosette in the first season and producing flowers and fruits and then dying in the second season.
- Botany A perennial plant, such as the English daisy, cultivated as a biennial.