The Collaborative International Dictionary of English v.0.48:

Stubborn \Stub"born\, a. [OE. stoburn, stiborn; probably fr. AS.
   styb a stub. See Stub.]
   Firm as a stub or stump; stiff; unbending; unyielding;
   persistent; hence, unreasonably obstinate in will or opinion;
   not yielding to reason or persuasion; refractory; harsh; --
   said of persons and things; as, stubborn wills; stubborn ore;
   a stubborn oak; as stubborn as a mule. "Bow, stubborn knees."
   --Shak. "Stubborn attention and more than common
   application." --Locke. "Stubborn Stoics." --Swift.
   [1913 Webster]

         And I was young and full of ragerie [wantonness]
         Stubborn and strong, and jolly as a pie. --Chaucer.
   [1913 Webster]

         These heretics be so stiff and stubborn. --Sir T. More.
   [1913 Webster]

         Your stubborn usage of the pope.         --Shak.
   [1913 Webster]

   Syn: Obstinate; inflexible; obdurate; headstrong; stiff;
        hardy; firm; refractory; intractable; rugged;
        contumacious; heady.

   Usage: Stubborn, Obstinate. Obstinate is used of either
          active or passive persistence in one's views or
          conduct, in spite of the wishes of others. Stubborn
          describes an extreme degree of passive obstinacy. --
          Stub"born*ly, adv. -- Stub"born*ness, n.
          [1913 Webster]

WordNet (r) 3.0 (2006):

stubborn
    adj 1: tenaciously unwilling or marked by tenacious
           unwillingness to yield [syn: stubborn, obstinate,
           unregenerate] [ant: docile]
    2: not responding to treatment; "a stubborn infection"; "a
       refractory case of acne"; "stubborn rust stains" [syn:
       refractory, stubborn]

Moby Thesaurus II by Grady Ward, 1.0:

189 Moby Thesaurus words for "stubborn":
   adamant, adamantine, adherent, adhesive, assiduous, balking, balky,
   bigoted, bulldogged, bulldoggish, bulldoggy, bulletheaded,
   bullheaded, cantankerous, cartilaginous, case-hardened, chewy,
   clingy, cohesive, constant, continuing, contumacious, coriaceous,
   determined, diligent, dogged, dogmatic, dour, durable, enduring,
   faithful, fanatic, fibrous, firm, fundamentalist, gluey, glutinous,
   gristly, gummy, hard, hardheaded, hardy, headstrong, hidebound,
   immovable, immutable, impliable, inalterable, indefatigable,
   indomitable, inductile, industrious, inelastic, inexorable,
   inextensible, inextensile, inextensional, inflexible, insistent,
   insubordinate, intolerant, intractable, intractile, intransigent,
   invincible, iron, ironbound, ironclad, ironhanded, irresilient,
   lasting, leatherlike, leathery, loyal, mulish, muscle-bound,
   never-tiring, nonelastic, nonstretchable, obdurate, obstinate,
   opinionated, ornery, orthodox, overzealous, patient,
   patient as Job, permanent, perseverant, persevering, persistent,
   persisting, pertinacious, pigheaded, plodding, plugging,
   preoccupied, procrustean, purist, puristic, puritan, puritanic,
   rapt, rebellious, recalcitrant, refractory, relentless, resistant,
   resolute, restive, rigid, rigorist, rigoristic, rigorous,
   rockbound, ropy, sedulous, self-adhesive, self-willed, set, sinewy,
   single-minded, sleepless, slogging, stable, steadfast, steady,
   stickable, sticky, stiff, stiff-necked, straightlaced, straitlaced,
   stringy, strong, strong-willed, strongheaded, stunt, sulky, sullen,
   tacky, tenacious, tireless, tough, tough as leather, unabating,
   unalterable, unbending, uncompromising, unconquerable,
   uncooperative, undaunted, undiscouraged, undrooping, unextendible,
   unextensible, unfailing, unfaltering, unflagging, unflexible,
   unflinching, ungiving, unintermitting, uninterrupted, unlimber,
   unmalleable, unnodding, unpliable, unpliant, unregenerate,
   unrelaxing, unrelenting, unremitting, unsleeping, unswerving,
   untiring, untractable, unwavering, unwearied, unwearying,
   unwinking, unyielding, utterly attentive, vigorous, viscid,
   wayward, weariless, willful, wiry