1. Holding or adhering obstinately to any opinion, purpose, or design.
2. Stubbornly or perversely persistent.
Pertinacious is from Latin pertinax, "having a firm hold, obstinate," from per-, "thoroughly" + tenax, "holding fast, tenacious," from tenere, "to hold."
When he made up his little [mind] to have or to do anything, all the king's horses and all the king's men could not change that pertinacious little mind.
-- Louisa May Alcott, Good Wives