Source : Webster's Revised Unabridged Dictionary (1913)

Bullheaded \Bull"head`ed\ (b[.u]l"h[e^]d`[e^]d), a.
   Having a head like that of a bull. Fig.: Headstrong;
   obstinate; dogged.

Source : WordNet®

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