Synonyms for Pertinacious (same or very similar meaning)
WordNet sense 1 (stubbornly unyielding):
dogged, dour, tenacious, unyielding, doggedWordNet sense 2 (tenaciously unwilling or marked by tenacious unwillingness to yield):
obstinate, stubborn, unregenerateFrom the ODE community, based on WordNetadd/edit