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

• outvote
• outwait
• outward
• outward-bound
• outward-developing
• outward-moving
• outwardly
• outwardness
• outwards
• outwear
• outweigh
• outweird
• outwit
• outwith
• outwork
• ouzel
• ouzo
• OV
• oval
• oval kumquat
• Oval Office
• oval window
• oval-bodied
• oval-fruited
• oval-shaped