Shotgun

wiktionary

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From shot +‎ gun. Front passenger seat sense comes from ride shotgun.

etymonline

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shotgun (n.)

1821, American English, from shot (n.) in the sense of "lead in small pellets" (1770) + gun (n.). As distinguished from a rifle, which fires bullets. Shotgun wedding is attested by 1903, American English. To ride shotgun is by 1905, from custom of having an armed man beside the driver on the stagecoach in the Old West to ward off trouble.