fail safe

/ˈfeɪlˌseɪf/
noun
  1. A system or mechanism that ensures safety if something fails.
    • The airplane has multiple fail-safes to prevent engine failure.
    • Engineers added a fail-safe to the bridge to handle extreme winds.
    • The security system includes a fail-safe that locks all doors during a fire.
adjective
  1. Designed to stop working or return to a safe condition if something goes wrong.
    • The software includes a fail-safe mode that prevents data corruption.
    • The nuclear reactor has a fail-safe system that shuts it down automatically.
    • All elevators are equipped with fail-safe brakes in case of power loss.
  2. Certain to succeed or be effective; guaranteed not to fail.
    • The recipe is fail-safe—even beginners can make it perfectly.
    • She thought her plan was fail-safe, but unexpected problems arose.
    • He claimed his investment strategy was fail-safe, but it still lost money.