Definition of "obdurate"

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

1594–1597, Richard Hooker, edited by J[ohn] S[penser], Of the Lawes of Ecclesiastical Politie, […], London: […] Will[iam] Stansby [for Matthew Lownes], published 1611, (please specify the page)

Art thou obdurate, flinty, hard as steel,Nay, more than flint, for stone at rain relenteth?

c. 1591–1592 (date written), William Shakespeare, “The Third Part of Henry the Sixt, […]”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act I, scene iv]

[…] round he throws his baleful eyesThat witness'd huge affliction and dismayMixt with obdurate pride and stedfast hate:

1667, John Milton, “Book I”, in Paradise Lost. […], London: […] [Samuel Simmons], […]; republished as Paradise Lost in Ten Books: […], London: Basil Montagu Pickering […], 1873, lines 56–58

But custom maketh blind and obdurateThe loftiest hearts.

1818, Percy Bysshe Shelley, “(please specify the page)”, in The Revolt of Islam; […], London: […] [F]or C[harles] and J[ames] Ollier, […]; by B. M‘Millan, […], stanza 9

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.

2011 February 12, Les Roopanarine, “Birmingham 1 - 0 Stoke”, in BBC‎

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.

2017 September 7, Ferdinand Mount, “Umbrageousness”, in London Review of Books‎

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

2012, Stephen King, 11/22/63, page 827

I fear the gentleman to whom Miss Amelia's letters were addressed was rather an obdurate critic.

1847 January – 1848 July, William Makepeace Thackeray, chapter 13, in Vanity Fair […], London: Bradbury and Evans […], published 1848