undoubtedly; unmistakably; without a doubt
Emphatic adverbial phrase meaning something is clearly the case and cannot be mistaken for anything else. Often used in formal or written contexts.
His talent is undoubtedly genuine.
The painting was appraised as unmistakably the work of a master.
Standard kanji spelling for this fixed adverbial phrase.
From the verb 紛う (まごう, 'to be mistaken for') in its negative continuative form 紛う方 (まごうかた, 'way of mistaking') + なく ('without'), literally 'without a way to mistake'.