fail-safe Synonyms

error failover airtight backup unpassable unfailing unerring trusty trustworthy tested sure steady well-tried confirmed foolproof be money in the bank as good as your word safety device tried and true surefire sure-fire idiot-proof fallback failsafe defectless steadfast stable device dependable covered confident complete checked certified certain buffer attested effective emergency flawless secure safety safeguard safe reliable protection protected insurance infallible guaranteed approved