Same word as outbreak:

beginning, blowup, brawl, break, breaking, burst, bursting, commencement, commotion, convulsion, crack, crash, dawn, detonation, discharge, disorder, disruption, ebullition, effervescence, epidemic, eruption, explosion, fit, flare-up, flash, fury, gush, gushing, insurrection, irruption, mutiny, onset, outburst, outpouring, paroxysm, plague, rebellion, rending, revolution, roar, sally, sortie, spasm, spurt, storm, sundering, surge, thunder, tumult, uprising, volley