1. Occurring every second year
   - biennial 
2. Occurring or payable twice each year
   - semiannual, biannual, half-yearly

1. Every two years
   - biennially 
2. Twice a year
   - semiannually

See also: periodic, periodical

• window-shop
• window-shopper
• window-washing
• windowless
• windowpane
• windowpane oyster
• Windows
• windowsill
• windpipe
• windrow
• windscreen
• windscreen wiper
• windshield
• windshield wiper
• windsock
• Windsor
• Windsor chair
• Windsor green
• Windsor knot
• Windsor tie
• windstorm
• windsurf
• windsurfer
• windswept
• windtalker