Synonyms and related words :
adamant, adamantine, cast-iron, close, dour, firm, flinty, grim, hard, hard-core, immovable, immutable, implacable, impliable, inductile, inelastic, inexorable, inextensible, inextensile, inextensional, inflexible, intractable, intractile, intransigent, iron, irreconcilable, irresilient, mean, miserly, niggardly, nonelastic, nonstretchable, parsimonious, penurious, relentless, rigid, rigorous, rock-ribbed, save-all, steely, stern, stiff, stubborn, tight, tightfisted, unaffected, unalterable, unbending, unchangeable, uncompromising, unextendible, unextensible, unflexible, unlimber, unmalleable, unmoved, unpliable, unpliant, unrelenting, untractable, unyielding