Synonyms to rock-ribbed

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, relentless, rigid, rigorous, rock, 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, crystal, Benzedrine, Benzedrine pill, C, Dexamyl, Dexamyl pill, Dexedrine, Dexedrine pill, Methedrine, amphetamine, amphetamine sulfate, avalanche, blizzard, clear, clear as crystal, clear-cut, cocaine, coke, craggy, crystal-clear, crystalline, dextroamphetamine sulfate, diaphane, diaphanous, driv