Synonyms and related words :
adamant, asleep, benumbed, bony, brazen, callous, calloused, case-hardened, cement, cemental, cold, cold of heart, coldblooded, coldhearted, concrete, conscienceless, corneous, dead, deadened, dense, diamondlike, dogged, dour, dull, dure, firm, flinthearted, flintlike, flinty, fundamentalist, granitelike, granitic, hard, hard as nails, hard of heart, hard-bitten, hard-boiled, hard-nosed, hard-set, hardened, hardhearted, heartless, hidebound, horny, immovable, impassible, impenitent, imperceptive, impercipient, impliable, indurated, inexorable, inflexible, insensate, insensible, insensitive, insentient, insolent, inured, iron, iron-hard, ironbound, ironclad, ironhanded, ironlike, lapideous, lithoid, lithoidal, lost to shame, marble, marblelike, mulish, muscle-bound, numb, numbed, obstinate, obtuse, orthodox, osseous, procrustean, purist, puristic, puritan, puritanic, relentless, resistant, resistive, rigid, rigorist, rigoristic, rigorous, rockbound, rocklike, rocky, seared, shameless, solid, steellike, steely, stiff, stiff-necked, stonelike, stony, stonyhearted, straightlaced, straitlaced, stubborn, thick-skinned, thick-witted, tough, unabject, unbending, unblushing, uncompassionate, uncompromising, uncontrite, unemotional, unfeeling, unfelt, unmelted, unmerciful, unnatural, unperceptive, unrelenting, unrepentant, unrepenting, unresponsive, unsoftened, unsympathetic, untouched, unyielding