Occurring every other year (8)
I believe the answer is:
biennial
'occurring every other year' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for biennial that I've seen before include "Two-yearly" , "Plant living two years" , "Taking place every other year" , "Happening every second year" , "Plant with a two-year life cycle" .)