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 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