副詞 forsooth:

1. an archaic word originally meaning `in truth' but now usually used to express disbelief

for.sooth

adv.（副詞）
In truth; indeed.
真的；確實(shí)

來(lái)源：
Middle English forsoth
中古英語(yǔ) forsoth
from Old English forsôth
源自 古英語(yǔ) forsôth
for [for] * see for
for [為了] *參見(jiàn) for
sôth [truth] * see sooth
sôth [真相] *參見(jiàn) sooth