Word Study
indubitably
CIDE DICTIONARY
indubitably, adv.
Undoubtedly; unquestionably; in a manner to remove all doubt. [1913 Webster]
"Oracles indubitably clear and infallibly certain." [1913 Webster]
THESAURUS
indubitably
actually, admittedly, assuredly, beyond doubt, beyond question, by all odds, certainly, clearly, decidedly, demonstrably, dollars to doughnuts, doubtless, doubtlessly, for a certainty, for real, in all conscience, in all likelihood, in all probability, incontestably, indeed, indisputably, irrefragably, irrefutably, like enough, likely, manifestly, most likely, no doubt, noticeably, observably, obviously, out of question, patently, positively, presumably, presumptively, probably, quite, really, sensibly, seriously, ten to one, truly, unambiguously, undeniably, undoubtedly, unmistakably, unquestionably, verily, very like, very likely, visibly, without doubtFor further exploring for "indubitably" in Webster Dictionary Online