Obdurate

[…] sometimes the very custom of evil making the heart obdurate against whatsoever instructions to the contrary […]

Art thou obdurate, flintie, hard as ſteele? / Nay more then flint, for ſtone at raine relenteth: […]

[…] round he throws his baleful eyes That witness'd huge affliction and dismay Mixt with obdurate pride and stedfast hate:

But custom maketh blind and obdurate The loftiest hearts.

Late the next afternoon Tarzan and his Waziri returned with the first load of “belongings,” and when the party saw the ancient ingots of virgin gold they swarmed upon the ape-man with a thousand questions; but he was smilingly obdurate to their appeals—he declined to give them the slightest clew as to the source of his immense treasure.

An injury-time goal from Nikola Zigic against an obdurate Stoke side gave Birmingham back-to back Premier League wins for the first time in 14 months.

What Tharoor dismisses as mere ‘positive by-products’ Lalvani sees as central to the India the British left behind: the botanic gardens, the forest conservancies, the Archaeological Survey of India (brainchild of the otherwise obdurate Curzon) and the free press.

The past is obdurate for the same reason a turtle's shell is obdurate: because the living flesh inside is tender and defenseless.