biyearly vs half-yearly

biyearly and half-yearly both are adjectives.

Word	Noun	Adjective	Verb	Adverb
biyearly	No	Yes	No	Yes
half-yearly	No	Yes	No	Yes

As adjectives, biyearly and half-yearly are synonyms defined as:

Other synonyms of biyearly include biannual, semiannual.

biyearly (adjective)	half-yearly (adjective)
occurring or payable twice each year	occurring or payable twice each year
occurring every second year

biyearly (adverb)	half-yearly (adverb)
every two years	every half year, every six months
twice a year