Etymology
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cock (n.2)

in various mechanical senses, such as "turn-valve of a faucet" (early 15c.), of uncertain connection with cock (n.1). Perhaps all are based on real or fancied resemblances not now obvious; German has hahn "cock" in many of the same senses.

The cock of a firearm, which when released by the action of the trigger discharges the piece, is from 1560s. Hence "position into which the hammer is brought by being pulled back to the catch" (1745). For half-cocked, see cock (v.).

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safety (n.)

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]
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