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reason; significance; cause
piece of information that one has heard; I hear that ...; it is said that ...
彼が怒った由を聞いてみた。
I asked about the reason he got angry.
事故の由を調べるのに時間がかかる。
It takes time to investigate the cause of the accident.
この祭りの由はとても古いらしい。
The origin of this festival is apparently very old.