early 14c., savete, "freedom or immunity from harm or danger; an unharmed or uninjured state or condition," from Old French sauvete, salvete "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"). From late 14c. as "means or instrument of safety, a safeguard."
The meaning "trigger-lock on a gun" is attested by 1881, perhaps short for safety-lock (1877), etc. As a North American football position, by 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) is by 1916, later of aerial circus performances (1920s); figurative use is by 1950. Safety-bicycle as a name for the modern type, with low, equal-sized wheels and a driving mechanism, is by 1866. Safety-razor is by 1877. A safety-belt (1840) was at first for window washers and firefighters; it was used of restraining straps for airplane pilots by 1911, extended to automobiles by 1948. Safety first as an accident-prevention slogan first recorded 1873.
Safety first, and saving of fuel second, should be the rule in steam engineering. [Scientific American, June 15, 1861]