The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   2. Resolute; persevering; constant; steady.
      [1913 Webster]

            Diligence is a steady, constant, and pertinacious
            study.                                --South.
      [1913 Webster]

   Syn: Obstinate; stubborn; inflexible; unyielding; resolute;
        determined; firm; constant; steady.
        [1913 Webster] -- Per`ti*na"cious*ly, adv. --
        Per`ti*na"cious*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

pertinaciously
    adv 1: in a dogged and pertinacious manner; "he struggled
           pertinaciously for the new resolution"