You use ~ to describe something when you want to emphasize that it is definite and cannot be doubted. (FORMAL)
His brilliance renders this film an ~ classic.
= undeniable
ADJ emphasis
indubitably
His behaviour was indubitably ill-judged.
ADV
You use ~ to describe something when you want to emphasize that it is definite and cannot be doubted. (FORMAL)
His brilliance renders this film an ~ classic.
= undeniable
ADJ emphasis
indubitably
His behaviour was indubitably ill-judged.
ADV
Collins COBUILD. Толковый словарь английского языка для изучающих язык Коллинз COBUILD (международная база данных языков Бирмингемского университета) . 2012