1. Every two years
   "this festival takes places biennially"
   - biyearly

See also: biennial

• third-degree burn
• third-dimensional
• third-dimensionality
• third-place finish
• third-rate
• third-rater
• third-year
• thirdhand
• thirdly
• thirst
• thirst for knowledge
• thirster
• thirstily
• thirstiness
• thirsty
• thirteen
• thirteenth
• thirties
• thirtieth
• thirty
• Thirty Years' War
• thirty-eight
• thirty-eighth
• thirty-fifth
• thirty-first