early 14c., from Old French sauvete "safety, safeguard; salvation; security, surety," earlier salvetet (11c., Modern French sauveté), from Medieval Latin salvitatem (nominative salvitas) "safety," from Latin salvus "uninjured, in good health, safe" (from PIE root *sol- "whole, well-kept"). Meaning "trigger-lock on a gun" is attested from 1881.
As a North American football position, first recorded 1931. As a type of score against one's own team, 1881. Safety-valve, which diminishes the risk of explosion, is from 1797; figurative sense recorded from 1818. Safety-net in literal sense (in machinery) by 1916, later of aerial circus performances (1920s); figurative use by 1950. Safety first as an accident-prevention slogan first recorded 1873.