obdurate (adj.)

mid-15c., "stubborn, inexorable, unyielding; hardened," especially against moral influences; "stubbornly wicked," from Latin obduratus "hardened," past participle of obdurare "harden, render hard; be hard or hardened; hold out, persist, endure," in Church Latin "to harden the heart against God," from ob "against" (see ob-) + durare "harden, render hard," from durus "hard," from PIE *dru-ro-, suffixed variant form of root *deru- "be firm, solid, steadfast." Variant opturate is from early 15c. in medicine in a literal sense of "stopped, obstructed."  Related: Obdurately; obdurateness.