The Collaborative International Dictionary of English v.0.48:

Obstinacy \Ob"sti*na*cy\, n. [See Obstinate.]
   1. A fixedness in will, opinion, or resolution that can not
      be shaken at all, or only with great difficulty; firm and
      usually unreasonable adherence to an opinion, purpose, or
      system; unyielding disposition; stubborness; pertinacity;
      persistency; contumacy.
      [1913 Webster]

            You do not well in obstinacy
            To cavil in the course of this contract. --Shak.
      [1913 Webster]

            To shelter their ignorance, or obstinacy, under the
            obscurity of their terms.             --Locke.
      [1913 Webster]

   2. The quality or state of being difficult to remedy,
      relieve, or subdue; as, the obstinacy of a disease or
      evil.
      [1913 Webster]

   Syn: Pertinacity; firmness; resoluteness; inflexibility;
        persistency; stubbornness; perverseness; contumacy.

   Usage: Obstinacy, Pertinacity. Pertinacity denotes great
          firmness in holding to a thing, aim, etc. Obstinacy is
          great firmness in holding out against persuasion,
          attack, etc. The former consists in adherence, the
          latter in resistance. An opinion is advocated with
          pertinacity or defended with obstinacy. Pertinacity is
          often used in a good sense; obstinacy generally in a
          bad one. "In this reply was included a very gross
          mistake, and if with pertinacity maintained, a capital
          error." --Sir T. Browne. "Every degree of obstinacy in
          youth is one step to rebellion." --South.
          [1913 Webster]

WordNet (r) 3.0 (2006):

obstinacy
    n 1: the trait of being difficult to handle or overcome [syn:
         stubbornness, obstinacy, obstinance, mulishness]
    2: resolute adherence to your own ideas or desires [syn:
       stubbornness, bullheadedness, obstinacy, obstinance,
       pigheadedness, self-will]

Moby Thesaurus II by Grady Ward, 1.0:

247 Moby Thesaurus words for "obstinacy":
   adhesiveness, antagonism, antipathy, application, assiduity,
   assiduousness, averseness, aversion, backwardness, bad blood,
   bloody-mindedness, bulldog tenacity, bullheadedness,
   cantankerousness, challenge, clashing, cohesiveness, collision,
   combative reaction, commitment, competition, complaint,
   concentration, conflict, consistency, constancy, contrariety,
   contrariness, contumaciousness, contumacy, counteraction,
   cross-purposes, cursoriness, decidedness, decision, decisiveness,
   dedication, defiance, defiance of authority, definiteness, demur,
   determinateness, determination, determinedness, devotion,
   diligence, disaccord, disagreement, disinclination, disobedience,
   dispute, disrelish, dissension, dissent, dissentience, distaste,
   dogged perseverance, doggedness, earnestness, endurance, energy,
   engrossment, enmity, fidelity, firmness, fixedness, foot-dragging,
   force, fortitude, fractiousness, friction, frowardness,
   fundamentalism, gluiness, glutinosity, grudging consent,
   grudgingness, gumminess, guts, gutsiness, hardiness, hardness,
   heartiness, hostility, imperviousness, impliability,
   indefatigability, indisposedness, indisposition, indocility,
   industriousness, industry, inexorability, inflexibility,
   inimicalness, insistence, insistency, intestinal fortitude,
   intractability, intractableness, intransigence, lack of enthusiasm,
   lack of zeal, loyalty, lustihood, lustiness, might, mightiness,
   mulishness, mutinousness, negativeness, negativism, nolition,
   noncooperation, obduracy, obdurateness, objection, obstinateness,
   obstreperousness, opposition, oppugnancy, orneriness, orthodoxy,
   passive resistance, patience, patience of Job, perfunctoriness,
   permanence, perseverance, persistence, persistency,
   pertinaciousness, pertinacity, perverseness, perversity,
   pigheadedness, plodding, plugging, potency, power, powerfulness,
   precisianism, preoccupation, protest, purism, puritanism, purpose,
   purposefulness, reaction, rebelliousness, rebuff, recalcitrance,
   recalcitrancy, recalcitration, refractoriness, refusal,
   relentlessness, reluctance, remonstrance, renitence, renitency,
   repellence, repellency, repugnance, repulse, repulsion, resistance,
   resoluteness, resolution, resolve, resolvedness, restiveness,
   retention, revolt, rigidity, rigidness, rigor, rigorousness,
   rivalry, robustness, ruggedness, sedulity, sedulousness, self-will,
   seriousness, sincerity, single-mindedness, singleness of purpose,
   slogging, slowness, snugness, stability, stalwartness, stamina,
   stand, staying power, steadfastness, steadiness,
   stick-to-itiveness, stickiness, sticking power, stiffness,
   stolidity, stoutness, strength, strength of will, stubbornness,
   sturdiness, sulk, sulkiness, sulks, sullenness, tackiness,
   tenaciousness, tenacity, tightness, tirelessness, total commitment,
   toughness, unbendingness, uncompromisingness, uncooperativeness,
   unenthusiasm, unimpressionability, uninfluenceability,
   unmovability, unpersuadability, unreceptiveness, unrelentingness,
   unremittingness, unresponsiveness, unruliness, unsuggestibility,
   unsusceptibility, unswayableness, unswerving attention,
   unwillingness, unyieldingness, vigor, vigorousness, viscidity,
   viscosity, vitality, vying, wildness, will, withstanding