Source : Webster's Revised Unabridged Dictionary (1913)

Unmerciful \Un*mer"ci*ful\, a.
   Not merciful; indisposed to mercy or grace; cruel; inhuman;
   merciless; unkind. -- {Un*mer"ci*ful*ly}, adv. --
   {Un*mer"ci*ful*ness}, n.

Source : WordNet®

unmercifully
     adv : without pity; in a merciless manner; "he was mercilessly
           trounced by his opponent in the House" [syn: {mercilessly},
            {pitilessly}, {remorselessly}]