The Collaborative International Dictionary of English v.0.48:

Obstinate \Ob"sti*nate\, a. [L. obstinatus, p. p. of obstinare
   to set about a thing with firmness, to persist in; ob (see
   Ob-) + a word from the root of stare to stand. See Stand,
   and cf. Destine.]
   1. Pertinaciously adhering to an opinion, purpose, or course;
      persistent; not yielding to reason, arguments, or other
      means; stubborn; pertinacious; -- usually implying
      unreasonableness.
      [1913 Webster]

            I have known great cures done by obstinate
            resolution of drinking no wine.       --Sir W.
                                                  Temple.
      [1913 Webster]

            No ass so meek, no ass so obstinate.  --Pope.
      [1913 Webster]

            Of sense and outward things.          --Wordsworth.
      [1913 Webster]

   2. Not yielding; not easily subdued or removed; as, obstinate
      fever; obstinate obstructions.
      [1913 Webster]

   Syn: Stubborn; inflexible; immovable; firm; pertinacious;
        persistent; headstrong; opinionated; unyielding;
        refractory; contumacious. See Stubborn.
        [1913 Webster] -- Ob"sti*nate*ly, adv. --
        Ob"sti*nate*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

obstinate
    adj 1: tenaciously unwilling or marked by tenacious
           unwillingness to yield [syn: stubborn, obstinate,
           unregenerate] [ant: docile]
    2: stubbornly persistent in wrongdoing [syn: cussed,
       obdurate, obstinate, unrepentant]
    3: resistant to guidance or discipline; "Mary Mary quite
       contrary"; "an obstinate child with a violent temper"; "a
       perverse mood"; "wayward behavior" [syn: contrary,
       obstinate, perverse, wayward]
    v 1: persist stubbornly; "he obstinates himself against all
         rational arguments"

Moby Thesaurus II by Grady Ward, 1.0:

281 Moby Thesaurus words for "obstinate":
   adamant, adherent, adhesive, adversary, adversative, adverse,
   alien, antagonistic, anti, antipathetic, antithetic, assiduous,
   balking, balky, beefy, bigoted, bloody-minded, bouncing, bound,
   bound and determined, bulldogged, bulldoggish, bulldoggy,
   bulletheaded, bullheaded, case-hardened, clashing, clingy,
   closed to, closed-minded, committed, competitive, con, conflicting,
   constant, continuing, contradictory, contrary, contumacious,
   costive, counter, crabbed, cross, deaf, decided, decisive,
   dedicated, definite, determined, devoted, diligent, disaccordant,
   disobedient, dissentient, dogged, dogmatic, doughty, dour, earnest,
   enduring, enemy, faithful, fanatic, firm, fixed, forceful,
   forcible, forcy, fractious, froward, full-blooded, full-strength,
   fundamentalist, gluey, glutinous, gummy, gutsy, gutty, hale, hard,
   hard as nails, hardheaded, hardy, headstrong, hearty, hefty,
   hidebound, hostile, husky, immovable, immutable, impersuadable,
   impersuasible, impervious, impliable, inalterable, indefatigable,
   indisciplined, indomitable, industrious, inexorable, inflexible,
   inimical, insistent, intolerant, intractable, intransigent,
   invincible, iron, iron-hard, ironbound, ironclad, ironhanded,
   lasting, lawless, loyal, lusty, mighty, mulish, muscle-bound,
   naughty, negative, nervy, never-tiring, nonconforming,
   noncooperative, obdurate, obstipated, opinionated, opponent,
   opposed, opposing, opposite, oppositional, oppositive, oppugnant,
   orthodox, overthwart, overzealous, patient, patient as Job,
   permanent, perseverant, persevering, persistent, persisting,
   pertinacious, perverse, pigheaded, plodding, plugging, potent,
   powerful, preoccupied, procrustean, puissant, purist, puristic,
   puritan, puritanic, purposeful, rapt, rebellious, recalcitrant,
   recusant, red-blooded, refractory, relentless, renitent, repugnant,
   resistant, resolute, resolved, restive, rigid, rigorist,
   rigoristic, rigorous, rival, robust, robustious, rockbound, rugged,
   sedulous, self-adhesive, self-willed, serious, set, sincere,
   single-minded, sleepless, slogging, sot, stable, stalwart, staunch,
   steadfast, steady, steely, stickable, sticky, stiff, stiff-necked,
   stony, stout, straightlaced, straitlaced, strapping, strong,
   strong as brandy, strong as strong, strong-willed, strongheaded,
   stubborn, sturdy, sulky, sullen, tacky, tenacious, tireless, tough,
   transgressive, unabating, unamenable, unbending, unchangeable,
   uncomplying, uncompromising, unconquerable, uncooperative,
   undaunted, undisciplined, undiscouraged, undrooping, unduteous,
   undutiful, unfailing, unfaltering, unfavorable, unflagging,
   unflinching, unfriendly, unimpressionable, uninfluenceable,
   unintermitting, uninterrupted, unmovable, unmoving, unnodding,
   unpersuadable, unpliable, unpliant, unpropitious, unreceptive,
   unregenerate, unrelaxing, unrelenting, unremitting, unresponsive,
   unsleeping, unsubmissive, unsuggestible, unsusceptible, unswayable,
   unswerving, untiring, unwavering, unwearied, unwearying, unwinking,
   unyielding, utterly attentive, vigorous, violative, viscid,
   wayward, weariless, wholehearted, willful, withstanding,
   wrongheaded



The Devil's Dictionary (1881-1906):

OBSTINATE, adj.  Inaccessible to the truth as it is manifest in the
splendor and stress of our advocacy.
    The popular type and exponent of obstinacy is the mule, a most
intelligent animal.