Forsooth

наречие [ироническое] несомненно, без сомнения, поистине Синоним(ы): undoubtedly, without question, without doubt

Большой англо-русский словарь

Forsooth

adverb Etymology: Middle English for soth, from Old English forsōth, from for + sōth sooth in truth; indeed — often used to imply contempt or doubt

Энциклопедический словарь Мерриама-Вебстера