doubtlessly

Etymology
From, , equivalent to.

Adverb

 * 1)  Without question; indubitably.
 * There are doubtlessly more insects than mammals.
 * 1)  Without feeling doubt, without misgivings.

Usage notes
Sometimes considered a redundancy, as doubtless (without the -ly suffix) functions as an adverb with an identical meaning. The synonyms indubitably, undoubtedly, and unquestionably all require the -ly suffix.