biennial

Concise Oxford English Dictionary © 2008 Oxford University Press:
biennial /bʌɪˈɛnɪəl/

▶adjective

• 1 taking place every other year. Compare with biannual.

• 2 (of a plant) taking two years to grow from seed to fruition and die. Compare with annual, perennial.

▶noun

• 1 a biennial plant.

• 2 an event celebrated or taking place every two years.

– derivatives
biennially adverb.

– origin C17: from L. biennis (from bi- ‘twice’ + annus ‘year’) + -al.