Lewis & Short

pertĭnācĭa, ae, f. [pertinax], perseverance, constancy, in a good sense; and (more freq.) in a bad sense, obstinacy, pertinacity (syn.: perseverantia, pervicacia): dicitur quom demonstratur in quo non debet pertendi et pertendit, pertinaciam esse; in quo oportet manere, si in eo perstet, perseverantia sit, Varr. L. L. 5, § 2 Müll.; cf.: unicuique virtuti finitimum vitium reperietur, ut pertinacia, quae perseverantiae finitima est, Cic. Inv. 2, 54, 165; v. Att. ap. Non. 432, 32 sq.: certamen instituit non pertinaciā et studio vincendi, sed, etc., Cic. Ac. 1, 12, 44: desistere pertinaciā, Caes. B. G. 1, 42: pertinaciae finem facere, id. B. C. 3, 10: muliebri pertinacia accendi, Tac. H. 4, 56: pertinaciam alicujus vincere, id. A. 2, 81.
In a good sense, Liv. 42, 62: patientia et pertinacia hostis, Suet. Caes. 68: in evitando inevitabili malo, Sen. Q. N. 4, praef. 12: auctorum pertinacia, steadfast opinion, Plin. 37, 3, 13, § 52.
Personified, the sister of Æther and Dies, Cic. N. D. 3, 17, 44.