(superl.) Consisting of, composed of, abounding in, or resembling, flint; as, a flinty rock; flinty ground; a flinty heart.

Philistine adamant adamantine bony bowelless callous calloused case-hardened cast-iron cement cemental concrete constant corneous cruel dense diamondlike dog-eat-dog dour dure firm fixed flintlike granitelike granitic grim hard hard as nails hard-core hardened hardhearted harsh heartless horny immovable immutable impervious implacable impliable inclement indurated inelastic inexorable inflexible insensitive intransigent inured iron iron-hard ironlike irreconcilable lapideous lithic lithoid lithoidal loyal marble marblelike merciless obdurate osseous pachydermatous petrified petrogenic pitiless proof against relentless remorseless resistant resistive rigid rigorous rock rock-ribbed rocklike rocky ruthless set settled slaty solid sot staunch steadfast steady steeled against steellike steely stern stiff stone stonelike stony thick-skinned tough TRUE unaffected unalterable unbending unchangeable uncompassionate uncompassioned uncompromising undeflectable unfeeling unflappable unforgiving ungiving unmerciful unmoved unpitiful unpitying unrelenting unremorseful unshaken unswerving unsympathetic unsympathizing unyielding without mercy