The Collaborative International Dictionary of English v.0.48:

Pig-headed \Pig"-head`ed\, a.
   Having a head like a pig; hence, figuratively: stupidity
   obstinate; perverse; stubborn. --B. Jonson. --
   Pig"-head`ed*ness, n.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "pigheaded":
   balking, balky, bigoted, bulldogged, bulletheaded, bullheaded,
   case-hardened, dogged, dogmatic, fanatic, hardheaded, headstrong,
   intolerant, intractable, mulish, obstinate, opinionated,
   overzealous, persevering, pertinacious, perverse, restive,
   self-willed, set, stiff-necked, strong-willed, strongheaded,
   stubborn, sulky, sullen, tenacious, uncooperative, unregenerate,
   unyielding, willful