What is not relenting; unyielding; rigid; hard; stern; cruel. -- Un`re*lent"ing*ly, adv. -- Un`re*lent"ing*ness, n called?

unrelenting — Not relenting; unyielding; rigid; hard; stern; cruel. -- Un`re*lent"ing*ly, adv. -- Un`re*lent"ing*ness, n. (Webster's 1913.)

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