Consisting of or having the hardness of adamant.

Roget 159: strong, mighty, vigorous, forcible, hard, adamantine, stout, robust, sturdy, hardy, powerful, potent, puissant, valid.    resistless, irresistible, invincible, proof against, impregnable, unconquerable, indomitable, dominating, inextinguishable, unquenchable; incontestable; more than a match for; overpowering, overwhelming; all powerful, all sufficient; sovereign.    able-bodied; athletic; Herculean, Cyclopean, Atlantean^†; muscular, brawny, wiry, well-knit, broad-shouldered, sinewy, strapping, stalwart, gigantic.    manly, man-like, manful; masculine, male, virile.    unweakened^†, unallayed, unwithered^†, unshaken, unworn, unexhausted^†; in full force, in full swing; in the plenitude of power.    stubborn, thick-ribbed, made of iron, deep-rooted; strong as a lion, strong as a horse, strong as an ox, strong as brandy; sound as a roach; in fine feather, in high feather; built like a brick shithouse; like a giant refreshed.    ... show more

Having the hardness of a diamond.

Impervious to pleas, persuasion, requests, reason.

synonyms: adamant, inexorable, intransigent.

Roget 323: hard, rigid, stubborn, stiff, firm; starch, starched; stark, unbending, unlimber, unyielding; inflexible, tense; indurate, indurated; gritty, proof.    adamant, adamantine, adamantean^†; concrete, stony, granitic, calculous, lithic^†, vitreous; horny, corneous^†; bony; osseous, ossific^†; cartilaginous; hard as a rock etc. n.; stiff as buckram, stiff as a poker; stiff as starch, stiff as as board.    ... show more