Source : Webster's Revised Unabridged Dictionary (1913)

Overpowering \O`ver*pow"er*ing\, a.
   Excelling in power; too powerful; irresistible. --
   {O`ver*pow"er*ing*ly}, adv.

Source : WordNet®

overpoweringly
     adv : incapable of being resisted; "the candy looked
           overwhelmingly desirable to the dieting man" [syn: {overwhelmingly},
            {irresistibly}]