noun, adverb
one by one; separately; individually
Describes doing something for each item or person separately, often with a nuance of thoroughness or, in negative contexts, annoyance at having to deal with every single thing.
彼は書類をいちいち確認した。
He checked the documents one by one.
いちいち文句を言わないでください。
Please don't complain about every little thing.
noun, adverb
every single; each and every; without omission
Emphasizes that no item is left out; often used in negative sentences or when expressing that something is done exhaustively, sometimes with a critical tone.
彼はいちいちのことに口を出す。
He butts in on every single thing.
いちいち説明する必要はない。
There's no need to explain each and every detail.