nail down (v.)

• ascertain
• assure
• balance
• ballast
• certify
• cinch
• clinch
• counterbalance
• decide
• demonstrate
• determine
• ensure
• establish
• firm
• fix
• follow
• freeze
• hold
• immobilize
• insure
• keep
• prove
• reassure
• retain
• settle
• show
• stabilize
• steady
• stick
• transfix