WordNet sense 1 (the act of firing weapons or artillery at an enemy):

fire

WordNet sense 2 (the act of setting something on fire):

ignition, inflammation, kindling, lighting

WordNet sense 3 (the termination of someone's employment (leaving them free to depart)):

discharge, dismissal, liberation, release, sack, sacking, dismission, discharge, release

WordNet sense 4 (the act of discharging a gun):

firing off