adv. 25B6; adverb UNDOUBTEDLY, indubitably, doubtlessly, no doubt; unquestionably, indisputably, undeniably, incontrovertibly, irrefutably; certainly, surely, of course, indeed.
DOUBTLESS
Meaning of DOUBTLESS in English
Concise Oxford thesaurus English vocabulary. Краткий оксфордский словарь английского языка тезаурус. 2012