Source : Webster's Revised Unabridged Dictionary (1913)

Remorseless \Re*morse"less\, a.
   Being without remorse; having no pity; hence, destitute of
   sensibility; cruel; insensible to distress; merciless.
   ``Remorseless adversaries.'' --South. ``With remorseless
   cruelty.'' --Milton.

   Syn: Unpitying; pitiless; relentless; unrelenting;
        implacable; merciless; unmerciful; savage; cruel. --
        {Re*morse"less*ly}, adv. -- {Re*morse"less*ness}, n.

Source : WordNet®

remorseless
     adj : without mercy or pity; "an act of ruthless ferocity"; "a
           monster of remorseless cruelty" [syn: {pitiless}, {ruthless},
            {unpitying}]