mulish

from WordNet (r) 3.0 (2006)

mulish
    adj 1: unreasonably rigid in the face of argument or entreaty or
           attack [syn: {hardheaded}, {mulish}]

from The Collaborative International Dictionary of English v.0.48

Mulish \Mul"ish\ (m[=u]l"[i^]sh), a.
   Like a mule; sullen; stubborn. -- {Mul"ish*ly}, adv. --
   {Mul"ish*ness}, n.
   [1913 Webster]

from Moby Thesaurus II by Grady Ward, 1.0

61 Moby Thesaurus words for "mulish":
      asinine, balking, balky, bigoted, bovid, bovine, bulldogged,
      bulletheaded, bullheaded, caprid, caprine, case-hardened, cowish,
      cowlike, deerlike, dogged, dogmatic, equestrian, equine, fanatic,
      fixed, goatish, goatlike, hardheaded, headstrong, hircine, hoggish,
      hoofed, horsy, intolerant, obstinate, opinionated, overzealous,
      ovine, persevering, pertinacious, perverse, piggish, pigheaded,
      refractory, restive, ruminant, self-willed, set, sheepish,
      sheeplike, stiff-necked, strong-willed, strongheaded, stubborn,
      sulky, sullen, swinish, tenacious, uncooperative, ungovernable,
      ungulate, unregenerate, unruly, willful, wrongheaded