utterly unyielding in attitude or opinion in spite of all appeals, urgings, etc.

too hard to cut, break, or pierce.

any impenetrably or unyieldingly hard substance.

a legendary stone of impenetrable hardness, formerly sometimes identified with the diamond.

adjective

flexible , pliant , submissive , yielding , soft , supple

adjective

determined , firm , fixed , hanging tough , hard-nosed , immovable , inexorable , inflexible , insistent , intransigent , obdurate , pat * , relentless , resolute , rigid , set , set in stone , standing pat , stiff , stubborn , unbendable , unbending , uncompromising , unrelenting , unshakable , unswayable , adamantine , flinty , impenetrable , indestructible , rock-hard , tough , unbreakable , brassbound , die-hard , grim , implacable , incompliant , iron , remorseless , uncompliant , unyielding , hard , stony