Source : Webster's Revised Unabridged Dictionary (1913)

Unrelenting \Un`re*lent"ing\, a.
   Not relenting; unyielding; rigid; hard; stern; cruel. --
   {Un`re*lent"ing*ly}, adv. -- {Un`re*lent"ing*ness}, n.

Source : WordNet®

unrelenting
     adj 1: not to be placated or appeased or moved by entreaty; "grim
            determination"; "grim necessity"; "Russia's final
            hour, it seemed, approached with inexorable
            certainty"; "relentless persecution"; "the stern
            demands of parenthood" [syn: {grim}, {inexorable}, {relentless},
             {stern}, {unappeasable}, {unforgiving}]
     2: never-ceasing; "the relentless beat of the drums" [syn: {persistent},
         {relentless}]