Source : Webster's Revised Unabridged Dictionary (1913)

Thunderclap \Thun"der*clap`\, n.
   A sharp burst of thunder; a sudden report of a discharge of
   atmospheric electricity. ``Thunderclaps that make them
   quake.'' --Spenser.

         When suddenly the thunderclap was heard. --Dryden.

Source : WordNet®

thunderclap
     n 1: a single sharp crash of thunder
     2: a shocking surprise; "news of the attack came like a
        bombshell" [syn: {bombshell}, {thunderbolt}]