from The American Heritage® Dictionary of the English Language, 4th Edition
- adv. Certainly: The wind was doubtless a factor.
- adv. Presumably; probably: as you doubtless already know.
- adj. Certain; assured.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Characterized by or experiencing no doubt at all, certain; undoubted; undoubting.
- adv. Without doubt; very probably, in all likelihood; doubtlessly.
from the GNU version of the Collaborative International Dictionary of English
- adj. Free from fear or suspicion.
- adv. Undoubtedly; without doubt.
from The Century Dictionary and Cyclopedia
- Free from doubt; indubitable.
- Having no fear; free from fear of danger; secure.
- Without doubt; without objection or uncertainty; unquestionably; often, with weakened sense, presumably, probably.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- adv. without doubt; certainly
From doubt + -less. (Wiktionary)