Insensitive, Intransigent, Inured, Iron, Irreconcilable, Lead, Leaden, Livid, Loyal, Lusty, Marble, Mercurial, Mighty, Mousy, Nervy, Nickel, Obdurate, Obstinate, Pearl, Pearly, Pewter, Potent, Powerful, Puissant, Quicksilver, Relentless, Resistant, Resistive, Rigid, Rigorous, Robust, Rocky, Rugged, Sad, Set, Settled, Silver, Silvered, Silvery, Smoky, Sober, Solid, Sot, Stalwart, Staunch, Steadfast, Steady, Steel, Stern, Stiff, Stony, Stout, Strapping, Strong, Sturdy, Tin, Tinny, Tough, True, Unaffected, Unalterable, Unbending, Unchangeable, Uncompromising, Unmoved, Unrelenting, Unshaken, Philistine, Adamant, Ashen, Ashy, Beefy, Bony, Bouncing, Brass, Brassy, Brazen, Bronze, Callous, Calloused, Cement, Concrete, Constant, Copper, Coppery, Cuprous, Dapple, Dappled, Dense, Dingy, Dismal, Doughty, Dour, Dreary, Dull, Dusty, Ferrous, Firm, Fixed, Flinty, Forceful, Forcible, Gilt, Glaucous, Gold, Golden, Granitic, Grey, Grim, Grizzled, Grizzly, Gutsy, Hale, Hard, Hardened, Hardhearted, Hardy, Hearty, Hefty, Horny, Husky, Immovable, Immutable, Impervious, Implacable, Inelastic, Inexorable, Inflexible, Unswerving, Unyielding, Vigorous