adverb, noun which may take the genitive case particle 'no'
one by one; separately; in detail
Used for doing something to each item individually, or for examining things carefully one at a time. Can function adverbially or as a no-adjective.
I explained each problem carefully, one by one.
Please speak, paying attention to each and every word.
I checked the contents of the luggage one by one.
Each handmade bowl has a slightly different shape.
The teacher explained each point carefully, one by one.