UNQUESTIONABLY

decidedly, unquestionably, emphatically, definitely, in spades, by all odds

(adverb) without question and beyond doubt; “it was decidedly too expensive”; “she told him off in spades”; “by all odds they should win”

unquestionably, unimpeachably

(adverb) without question; “Fred Winter is unquestionably the jockey to follow”; “they hired unimpeachably first-rate faculty members”

Source: WordNet® 3.1

Etymology

Adverb

unquestionably (comparative more unquestionably, superlative most unquestionably)

without question; beyond doubt; indubitably.

(informal) OK, right-on

Source: Wiktionary

UNQUESTIONABLE

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