Synonyms and related words :
adamant, adamantine, at a standstill, bowelless, bulky, bullheaded, cast-iron, certain, closed to, complaining, constant, cruel, dense, disputatious, disputing, dissentient, dissenting, dog-eat-dog, dour, durable, enduring, fated, fateful, firm, fixed, flinty, fractious, frozen, fundamentalist, grim, hard, hard-core, hard-line, harsh, headstrong, heartless, heavy, hidebound, immobile, immotile, immotive, immovable, immutable, impenetrable, impersuadable, impersuasible, impervious, implacable, impliable, impregnable, inclement, incontestable, indefeasible, indomitable, inductile, inelastic, ineluctable, inescapable, inevasible, inevitable, inexorable, inexpugnable, inextensible, inextensile, inextensional, inflexible, insuperable, intractable, intractile, intransigent, invincible, inviolable, invulnerable, iron, ironbound, ironclad, ironfisted, ironhanded, irreconcilable, irremovable, irresilient, irresistible, irrevocable, lasting, loyal, massive, merciless, mortal, mulish, muscle-bound, necessary, noncooperative, nonelastic, nonstretchable, obdurate, objecting, obstinate, obstructive, on the barricades, orthodox, overpowering, overwhelming, pat, pertinacious, pigheaded, pitiless, procrustean, proof against, protesting, purist, puristic, puritan, puritanic, rebellious, recalcitrant, refractory, relentless, reluctant, remorseless, renitent, repellent, resistant, resisting, resistive, resistless, retardant, retardative, rigid, rigorist, rigoristic, rigorous, rock-ribbed, rockbound, rugged, ruthless, self-willed, set, settled, single-minded, solid, sot, sound, stable, standpat, stationary, staunch, steadfast, steady, steely, stern, stiff, stout, straightlaced, straitlaced, strong, stubborn, sturdy, sure, sure as death, sure as fate, tough, TRUE, unaffected, unalterable, unamenable, unappeasable, unassailable, unavoidable, unbeatable, unbending, unchangeable, uncompassionate, uncompassioned, uncompliant, uncompromising, unconquerable, uncontrollable, uncooperative, undeflectable, unextendible, unextensible, unfeeling, unflappable, unflexible, unflinching, unforgiving, ungiving, unimpressionable, uninfluenceable, unlimber, unmalleable, unmerciful, unmovable, unmoved, unmoving, unpersuadable, unpitiful, unpitying, unpliable, unpliant, unpreventable, unreceptive, unrelenting, unremorseful, unresponsive, unshaken, unstoppable, unsubduable, unsubmissive, unsuggestible, unsurmountable, unsusceptible, unswayable, unswerving, unsympathetic, unsympathizing, untractable, up in arms, well-built, well-constructed, well-founded, well-grounded, well-made, without mercy, withstanding