Pertinacious, a.
Etymology: [L. pertinax, -acis; per + tenax tenacious. See Per-, and Tenacious.]
1. Holding or adhering to any opinion, purpose, or design, with obstinacy; perversely persistent; obstinate; as, pertinacious plotters; a pertinacious beggar.
2. Resolute; persevering; constant; steady. Diligence is a steady, constant, and pertinacious study. South.
Syn. -- Obstinate; stubborn; inflexible; unyielding; resolute; determined; firm; constant; steady. -- Per`ti*na"cious*ly, adv. -- Per`ti*na"cious*ness, n.
Shades of meaning
Fernald has no entry of its own for pertinacious; he lists it under obstinate.
Where he writes about it:
Pertinacious demand is contrasted with obstinate refusal. — from obstinate