Source : Webster's Revised Unabridged Dictionary (1913)

Outburst \Out"burst`\, n.
   A bursting forth.

Source : WordNet®

outburst
     n 1: an unrestrained expression of emotion [syn: {effusion}, {gush},
           {blowup}, {ebullition}]
     2: a sudden violent happening; "an outburst of heavy rain"; "a
        burst of lightning" [syn: {burst}, {flare-up}]
     3: a sudden violent disturbance [syn: {tumultuous disturbance}]