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one-by-one; separately
every single; each and every; without omission; fully; in detail
いちいち細かく説明するのは正直面倒だ。
It is troublesome to explain everything one by one.
彼はいちいち細かいことを気にする。
He worries about every little thing.
いちいち確認しないと気が済まない。
I cannot rest until I check everything one by one.