Emily Dickinson Lexicon

PER-TI-NA'CIOUS, a. [L. pertinax; per and teneo, to hold.]

1. Holding or adhering to any opinion, purpose or design with obstinacy; obstinate; perversely resolute or persistent; as, pertinacious in opinion; a man of pertinacious confidence. – Walton.
2. Resolute; firm; constant; steady. Diligence is a steady, constant, pertinacious study. – South. [This word often implies a censurable degree of firmness or constancy, like obstinacy.]