pertinacity

英 [,pɜːtɪ'næsɪtɪ] 美 [,pɝtn'æsəti]

1. per- "very, completely" + tinac- + -ity.
2. => very firm, tenacious, steadfast, stubborn.

pertinacity (n.): c. 1500, from Middle French pertinacité (early 15c.), from Old French pertinace "obstinate, stubborn," from Latin pertinacem (nominative pertinax) "very firm, tenacious, steadfast, persevering," from per- "very" (see per) + tenax (see tenacious). It drove out earlier pertinacy (late 14c.).