Relentless
Constant
Synonyms Persistent, constant, continuous, lasting, steady, unabated, unbroken, incessant, unceasing, unending, unremitting, unrelieved, unfaltering, untiring, unswerving, persevering, resolute, dogged, tireless, patient, assiduous, tenacious, insistent, stubborn, obstinate, continuing, continual, non-stop, never-ending, uninterrupted, unabating, interminable, unstoppable, endless, perpetual, unrelenting, sustained, unflagging, unwavering, undeviating, determined, purposeful, single-minded, indefatigable, diligent, sedulous, pertinacious, importunate, intransigent, and obdurate.
Fierce
Synonyms Harsh, fierce, severe, punishing, merciless, ruthless, unsparing, hard-hearted, stony-hearted, with a heart of stone, cold-hearted, unfeeling, unsympathetic, lacking compassion, inflexible, uncompromising, unyielding, inexorable, grim, cruel, strict, remorseless, pitiless, unmerciful, heartless, hard, stony, cold-blooded, unforgiving, uncaring, uncharitable, unpitying, unbending, obdurate, unmoved, and implacable.
Example Sentences
The storm was relentlessly fierce.
Her efforts were relentless today.
They faced relentless financial struggles.
He showed relentless determination throughout.