Synonyms for Biyearly (same or very similar meaning)
WordNet sense 1 (occurring every second year):
biennialWordNet sense 2 (occurring or payable twice each year):
biannual, semiannualWordNet sense 3 (every two years):
bienniallyWordNet sense 4 (twice a year):
semiannuallyFrom the ODE community, based on WordNetadd/edit