pervicacious pur-vih-KAY-shus, adjective:
Refusing to change one’s ideas, behavior, etc.; stubborn; obstinate.
Pervicacious is from Latin pervicax, pervicac-, “stubborn, headstrong,” from root pervic- of pervincere, “to carry ones point, maintain ones opinion,” from per-, “through, thoroughly” + vincere, “to conquer, prevail against” + the suffix -ious, “characterized by, full of.”