1. a mechanism capable of returning to a safe state in case there is a failure or malfunction

1. guaranteed not to fail;

   "a fail-safe recipe for cheese souffle"
   

2. eliminating danger by compensating automatically for a failure or malfunction;

   "a fail-safe device in a nuclear weapon to deactivate it automatically in the event of accident"
   

1.有自动保险装置的;具有自动防故障性能的
Something that isfail-safe is designed or made in such a way that nothing dangerous can happen if a part of it goes wrong.

e.g. The camera has a built-in failsafe device which prevents it from working if the right signals aren't received.
照相机有内置自动防故障装置，该装置确保相机在未接到正确信号时不会启动。