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]

WordNet (r) 3.0 (2006):

pigheaded
    adj 1: obstinate and stupid [syn: bullheaded, bullet-headed,
           pigheaded]