pertinaciously
In a stubbornly resolute manner; tenaciously holding one's course of action or opinion.
Saint Augustine makes this difference betweene an heretike, and him that beleeves an heretike. The first begets or followes an errour pertinaciously.
Where it comes from
From pertinacious + -ly, from Latin pertināx, from per- (“very”) + tenāx (“tenacious”), from teneō (“to hold”).
Adapted from the Wiktionary entry pertinaciously (CC BY-SA 4.0).