Doubtlessly
The Century Dictionary and Cyclopedia
Unquestionably.
the GNU version of the Collaborative International Dictionary of English
adverb.
Unquestionably.
Wiktionary, Creative Commons Attribution/Share-Alike License
adverb.
Without question;
indubitably
.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
adverb.
without doubt; certainly