biyearly
     adj 1: occurring every second year; "they met at biennial
            conventions" [syn: {biennial}]
     2: occurring or payable twice each year [syn: {semiannual}, {biannual}]
     adv 1: every two years; "this festival takes places biennially"
            [syn: {biennially}]
     2: twice a year [syn: {semiannually}]
Source: WordNet® 2.0