曰く

プログレッシブ和英中辞典(第4版)

いわく【^×曰く】

❶〔言うことには〕

聖書にいわく
the Bible says...

❷〔理由，事情〕a reason

いわくがあって
for certain reasons

これにはいわくがある
There is a story about it.

どうもいわくがありそうだ
There seems to be something behind it.

彼女はいわくありげな目付きで彼を見た
She cast a meaningful glance at him.

いわく言い難い

いわく言い難い魅力
(an) indescribable charm

事情は複雑でいわく言い難い
The situation is too complicated for words.

いわく因縁

a complicated story

彼はこの事柄のいわく因縁を聞かせてくれた
He told me how the whole matter had come about.

それについてのいわく因縁は何も知らない
I have no idea 「how it all got started [what lies behind it].

いわく付き

いわく付きの女
a woman with a past

家賃が安いと思ったらやっぱりいわく付きの家だった
I thought the rent was low, and, sure enough, I later found out that the house had a story behind it.

出典　小学館「プログレッシブ和英中辞典(第4版)」