You use indubitable to describe something when you want to emphasize that it is definite and cannot be doubted.
His brilliance renders this film an indubitable classic.
His behaviour was indubitably ill-judged.
Translation English Cobuild Collins Dictionary
certain, evident, incontestable, incontrovertible, indisputable, irrefutable, obvious, open-and-shut, sure, unarguable, undeniable, undoubted, unquestionable, veritable
English Collins Dictionary - English synonyms & Thesaurus
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