Source : Webster's Revised Unabridged Dictionary (1913)

Irresistibly \Ir`re*sist"i*bly\, adv.
   In an irrestible manner.

Source : WordNet®

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