Source : Webster's Revised Unabridged Dictionary (1913)

Pertinacious \Per`ti*na"cious\, a.[L. pertinax, -acis; per +
   tenax tenacious. See {Per-}, and {Tenacious}.]
   1. Holding or adhering to any opinion, purpose, or design,
      with obstinacy; perversely persistent; obstinate; as,
      pertinacious plotters; a pertinacious beggar.

   2. Resolute; persevering; constant; steady.

            Diligence is a steady, constant, and pertinacious
            study.                                --South.

   Syn: Obstinate; stubborn; inflexible; unyielding; resolute;
        determined; firm; constant; steady. --
        {Per`ti*na"cious*ly}, adv. -- {Per`ti*na"cious*ness}, n.

Source : WordNet®

pertinaciously
     adv : in a dogged and pertinacious manner; "he struggled
           pertinaciously for the new resolution"