Source : Webster's Revised Unabridged Dictionary (1913)

Flabbergast \Flab"ber*gast\, v. t. [Cf. {Flap}, and {Aghast}.]
   To astonish; to strike with wonder, esp. by extraordinary
   statements. [Jocular] --Beaconsfield.

Source : WordNet®

flabbergast
     v : overcome with amazement; "This boggles the mind!" [syn: {boggle},
          {bowl over}]