noun

• (mechanics) A safety lock or safety catch: a mechanism on a weapon or dangerous equipment designed to prevent accidental firing or operation.
  "Be sure that the safety is set before proceeding."
• (sports)
  "He sacked the quarterback in the end zone for a safety."
• (sports)
  "The free safety made a game-saving tackle on the runner who had broken past the linebackers."
• (sports)
  "Boy wondered about that bunt. He had a notion Fowler would commit himself soon because time was on the go. But Fowler didn’t, making it another sweep of three Pirates. He had thus far given up only two safeties."

verb

• (transitive) To secure (a mechanical component, as in aviation) to keep it from becoming detached even under vibration.