doubtlessly

Doubtlessly means without doubt or certainly, functioning as an adverb to express confidence in a statement.

It is less common than its near-synonym undoubtedly, and some consider it nonstandard or awkward, preferring doubtless or undoubtedly instead.

She will doubtlessly arrive on time, as she always does.

The word emphasizes the speaker's certainty while acknowledging that doubt could theoretically exist.