Source : Webster's Revised Unabridged Dictionary (1913)

Insensibly \In*sen"si*bly\, adv.
   In a manner not to be felt or perceived; imperceptibly;
   gradually.

         The hills rise insensibly.               --Addison.

Source : WordNet®

insensibly
     adv : in a numb manner; without feeling; "I stared at him numbly"
           [syn: {numbly}]