one by one

Adv.	1.	one by one - in single file; "the prisoners came out one by one" Synonyms: one after another, one at a time
	2.	one by one - one piece at a time; "she sold the plates by the piece" Synonyms: by the piece
	3.	one by one - apart from others; "taken individually, the rooms were, in fact, square"; "the fine points are treated singly" Synonyms: individually, on an individual basis, separately, severally, singly

one after another, one at a time