Synonyms to relentless

adamant, adamantine, at a standstill, cast-iron, dour, firm, flintlike, flinty, frozen, granitelike, granitic, grim, hard, hard-core, immobile, immotile, immotive, immovable, immutable, implacable, impliable, inductile, inelastic, inexorable, inextensible, inextensile, inextensional, inflexible, intractable, intractile, intransigent, iron, irreconcilable, irremovable, irresilient, lithic, marblelike, nonelastic, nonstretchable, obdurate, pat, petrified, petrogenic, rigid, rigorous, rock, rock-ribbed, slaty, standpat, stationary, steely, stern, stiff, stone, stubborn, unaffected, unalterable, unbending, unchangeable, uncompromising, unextendible, unextensible, unflexible, ungiving, unlimber, unmalleable, unmovable, unmoved, unmoving, unpliable, unpliant, unrelenting, unswayable, untractable, unyielding, ardent, abandoned, ablaze, acquiescent, afire, aflame, aflicker, aglow, agog, agreeable, alacritous, alcoholic, alight, amative, amatory, amenable, amorous, and, anxious, assiduous, athirst, avid, baking, blazing, blistering, boiling, boiling over, breathless, broiling, burning, burning hot, candent, cand