1. Once in two years; at the return of two years.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• finnially,
• biannually,
• biennually,
• viennially,
• niennially,
• hiennially,
• giennially,
• buennially,
• bjennially,
• bkennially,
• boennially,
• b9ennially,
• b8ennially,
• biwnnially,
• bisnnially,
• bidnnially,
• birnnially,
• bienniallyy,
• Brennindly,
• biennaly

• biannual,
• biennial,
• biannually.