It means 'once in a while' or 'sometime in the past', referring to a time not too long ago.
曾曾经；几何若干、多少。才有多少时候。指没过多久。
宋·王安石《祭盛侍郎文》补官扬州，公得谢归。曾几何时，讣者来门。”
We used to be close friends in the past, but now we rarely meet.
Learn the next connected idiom: 曾几何时 (céng jǐ hé shí) → 时不我待 (shí bù wǒ dài)
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