WordWeb Online

1. Occurring every second year
   "they met at biyearly conventions"
   - biennial
    
2. Occurring or payable twice each year
   - semiannual, biannual, half-yearly

1. Every two years
   "this festival takes places biyearly"
   - biennially
    
2. Twice a year
   - semiannually

See also: periodic, periodical