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®

unrelentingly
     adv : in a relentless manner; "he worked relentlessly" [syn: {relentlessly}]