Definitions
1.nounA type of action where the pressure from the fired cartridge blows a sliding mechanism backward to extract the fired cartridge, chamber another cartridge, and cock the hammer.
2.nounAn unintended adverse result, especially of a political action.
3.nounThe act of shotgunning (inhaling from a pipe etc. and exhaling into another smoker's mouth).
4.nounOn a steam locomotive, the reversal of exhaust gases when the regulator is closed without using the blower; see Blowback (steam engine).