- 1taking place every other year:the first of a series of biennial exhibitionsCompare with biannual.
early 17th century: from Latin biennis (from bi- 'twice' + annus 'year') + -al
Biennial and biannual are often confused. Biennial means ‘occurring every two years’ (the biennial Ryder Cup tournament), while biannual means ‘twice a year’ (the solstice is a biannual event). See also bi- (usage).