Unrelentless vs. Relentless

Relentless (adjective)

Unrelenting or unyielding in severity

Relentless (adjective)

Unremitting, steady and persistent

Unrelentless (adjective)

relentless.

Relentless (adjective)

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.

Relentless (adjective)

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"

Relentless (adjective)

never-ceasing;

"the relentless beat of the drums"