Source : Webster's Revised Unabridged Dictionary (1913)

Bombshell \Bomb"shell`\, n.
   A bomb. See {Bomb}, n.

Source : WordNet®

bombshell
     n 1: an entertainer who has a sensational effect; "she was a
          blonde bombshell"
     2: a shocking surprise; "news of the attack came like a
        bombshell" [syn: {thunderbolt}, {thunderclap}]
     3: an explosive bomb or artillery shell