pertinaceous

Adjective

pertinacious (comparative more pertinacious, superlative most pertinacious)

1. Holding tenaciously to an opinion or purpose.
   • When that divine took his leave, not a little discomfited and amazed at the pertinacious obstinacy of the women, Laura repeated her embraces and arguments with tenfold fervour to Helen, who felt that there was a great deal of cogency in most of the latter.1848 November – 1850 December, William Makepeace Thackeray, chapter XXII, in The History of Pendennis. […], volume I, London: Bradbury and Evans, […], published 1849, →OCLC, page 205
2. Stubbornly resolute or tenacious.
   • [O]ne of the Dissenters, which I could, but forbear, to name appeared to Dr. Sanderson to be so bold, so troublesome, and so illogical in the dispute, as forced patient Dr. Sanderson, who was then Bishop of Lincoln, and a moderator with other Bishops, to say, with an unusual earnestness, "That he...1678, Izaak Walton, The life of Dr. Sanderson, late Bishop of Lincoln (London: Printed for Richard Marriot) [without pagination or sections]