WordWeb Online

1. Tenaciously unwilling or marked by tenacious unwillingness to yield
   - stubborn, obstinate
    
2. Not reformed morally or spiritually
   "unregenerate human nature"; "unregenerate conservatism"
   - unregenerated
    
3. Unrepentant and incapable of being reformed
   "an unregenerate criminal"
   - unreformable

See also: bloody-minded [Brit], bolshie [Brit], bolshy [Brit], bullet-headed, bullheaded, cantankerous, contrarious, cross-grained, cussed, determined, disobedient, dogged, dour, hardheaded, impenitent, incorrigible, inflexible, intractable, lost, mulish, obdurate, obstinate, persistent, pertinacious, pigheaded, stiff-necked, strong-minded, strong-willed, stroppy [Brit], sturdy, tenacious, uncompromising, unconverted, unpersuaded, unremorseful, unrepentant, unyielding

Antonym: regenerate