"biyearly" in the adjective sense
1. biennial, biyearly
occurring every second year
"they met at biennial conventions"
2. semiannual, biannual, biyearly, half-yearly
occurring or payable twice each year
"biyearly" in the adverb sense
1. biennially, biyearly
every two years
"this festival takes places biennially"
2. semiannually, biyearly
twice a year
Source: WordNet® (An amazing lexical database of English)
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