unquestionable in WordNet English dictionary

1. not counterfeit or copied
   "an authentic signature"; "a bona fide manuscript"; "an unquestionable antique"; "photographs taken in a veritable bull ring"
   authentic  bona fide  unquestionable  veritable 
   
2. incapable of being questioned
   "unquestionable authority"
   unquestionable 
   
3. not open to question
   "an unquestionable (or unequivocal) loss of prestige"
   unquestionable