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something heard for the first time; hearing something for the first time
その話は初耳で非常に驚いたのを覚えている。
I remember being very surprised as it was the first I'd heard of it.
彼が結婚していたとは初耳だったので驚いた。
I was surprised as I hadn't heard that he was married.
新しい規則が導入されたとは初耳なので教えてほしい。
This is the first I've heard of new rules being introduced, so please tell me.