For-sóþ

According to the Old English Dictionary:

for-sóþ

adv. FORSOOTH, truly, certainly; certe :-- Wite ðú forsóþ know thou assuredly, Bt. 14, 3; Fox 46, 16. Ic forsóþ wát vērum nōvi. Bd. 3, 13. S. 538, 33. Saga him forsóþ dic ergo illi, Bd. 5, 9; S. 622, 37. for-soþ