one by one; separately; individually.
先生はいちいち出席を取った。
The teacher took attendance one by one.
そんなにいちいち確認しなくても大丈夫だよ。
You don't need to check every little thing like that.
荷物は箱にいちいち入れてから運んだ。
I put the items into boxes one by one before carrying them.
every single; each and every; completely; in detail (often used critically to mean 'every little').
彼は会議の内容をいちいちメモしていた。
He was taking notes on every single detail of the meeting.
いちいち文句を言うのはやめてください。
Please stop complaining about every little thing.
説明書にはいちいち注意点が書かれている。
The manual lists cautionary points one after another.