D defs.my
Entry 2 senses Webster, 1913

Pertinacious

/pûr-tn-ā'shəs/ · Per·ti·na·cious · IPA /pɝtn̩ˈeɪʃəs/
01 a. Holding or adhering to any opinion, purpose, or design, with obstinacy; perversely persistent; obstinate; as, pertinacious plotters; a pert…
  1. 1.
    Holding or adhering to any opinion, purpose, or design, with obstinacy; perversely persistent; obstinate; as, pertinacious plotters; a pertinacious beggar.
  2. 2.
    Resolute; persevering; constant; steady.
    “Diligence is a steady, constant, and pertinacious study.” South.