(a.) Like a mule; sullen; stubborn.

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