Source : Webster's Revised Unabridged Dictionary (1913)

Flare-up \Flare"-up`\, n.
   A sudden bursting into flame; a flaring.

Flare-up \Flare"-up`\, n.
   A sudden burst of anger or passion; an angry dispute.
   [Colloq.]

Source : WordNet®

flare-up
     n : a sudden violent happening; "an outburst of heavy rain"; "a
         burst of lightning" [syn: {outburst}, {burst}]