I. adverb Date: 14th century without doubt, probably , II. adjective Date: 14th century free from doubt ; certain , ~ly adverb ~ness noun
DOUBTLESS
Meaning of DOUBTLESS in English
Merriam Webster. Explanatory English dictionary Merriam Webster. Толковый словарь английского языка Мерриам-Уэбстер. 2012