(a.) 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.

adamant adamantine ardent assiduous bound bound and determined bowelless cast-iron ceaseless certain committed constant continual continuing continuous cruel decided decisive dedicated definite determined devoted diligent dog-eat-dog dogged dour earnest enduring energetic faithful fated fateful ferocious fervent fierce firm flinty fundamentalist grim habitual hard hard-core hardworking harsh heartless hidebound immovable immutable implacable impliable inalterable incessant inclement indefatigable indefeasible indomitable industrious inelastic ineluctable inescapable inevasible inevitable inexorable inflexible inhuman insistent intractable intransigent invincible iron ironbound ironclad ironhanded irreconcilable irresistible irrevocable laborious lasting loyal merciless mortal muscle-bound necessary never idle never-tiring obdurate obstinate orthodox patient patient as Job permanent perpetual perseverant persevering persistent persisting pertinacious pitiless plodding plugging preoccupied procrustean purist puristic puritan puritanic purposeful rapt regular remorseless resistless resolute resolved rigid rigorist rigoristic rigorous rock-ribbed rockbound ruthless sedulous serious sincere single-minded sleepless slogging stable steadfast steady steely stern stiff stiff-necked straightlaced straitlaced strenuous strict stringent stubborn sure sure as death sure as fate tenacious tireless tough unabated unabating unaffected unalterable unappeasable unavoidable unbending unbroken unceasing unchangeable uncompassionate uncompassioned uncompromising unconquerable uncontrollable undaunted undeflectable undeviating undiscouraged undrooping unfailing unfaltering unfeeling unflagging unflinching unforgiving ungiving unintermitting uninterrupted unmerciful unmoved unmoving unnodding unpitiful unpitying unpreventable unrelaxing unrelenting unrelieved unremitting unremorseful unsleeping unsparing unstoppable unswerving unsympathetic unsympathizing untiring unwavering unwearied unwearying unwinking unyielding utterly attentive vehement weariless wholehearted without mercy zealous