Relentless \Re*lent"less\, a.
   Unmoved by appeals for sympathy or forgiveness; insensible to
   the distresses of others; destitute of tenderness;
   unrelenting; unyielding; unpitying; as, a prey to relentless
   despotism.
   
[1913 Webster]


         For this the avenging power employs his darts, . . .
         Thus will persist, relentless in his ire. --Dryden.
   
[1913 Webster]
 -- {Re*lentless*ly}, adv. --
   {Re*lentless*ness}, n.
   
[1913 Webster]