Source : Webster's Revised Unabridged Dictionary (1913)

Detestably \De*test"a*bly\, adv.
   In a detestable manner.

Source : WordNet®

detestably
     adv : in an offensive and hateful manner; "I don't know anyone who
           could have behaved so abominably" [syn: {repulsively},
           {abominably}, {odiously}]