UNQUESTIONABLE
unquestionable
(adjective) not open to question; “an unquestionable (or unequivocal) loss of prestige”
authentic, bona fide, unquestionable, veritable
(adjective) not counterfeit or copied; “an authentic signature”; “a bona fide manuscript”; “an unquestionable antique”; “photographs taken in a veritable bull ring”
unquestionable
(adjective) incapable of being questioned; “unquestionable authority”
Source: WordNet® 3.1
Etymology
Adjective
unquestionable (comparative more unquestionable, superlative most unquestionable)
undeniable, obvious
Synonym: inquestionable
Source: Wiktionary
Un*ques"tion*a*ble, a.
1. Not questionable; as, an unquestionable title.
2. Not inviting questions or conversation. [R.] Shak.
– Un*ques"tion*a*bly, adv.
Source: Webster’s Unabridged Dictionary 1913 Edition