one by one

one by one

In individual succession, with each person or thing following another in order. The children walked silently, one by one, into the schoolhouse to begin their lesson. The usher asked the theater patrons to exit the theater one by one.
See also: by, one
Farlex Dictionary of Idioms.

one by one

 and one at a time
the first one, then the next one, then the next one, etc.; each in turn. I have to deal with problems one by one. I can't handle them all at once. Okay, just take things one at a time. The children came into the room one by one.
See also: by, one
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

one by one

Also, one at a time. Individually in succession, as in The ducklings jumped into the pond one by one, or One at a time they went into the office. Formerly also put as one and one and one after one, this idiom dates from about a.d. 1000.
See also: by, one
The American Heritage® Dictionary of Idioms by Christine Ammer.

ˌone by ˈone

one after another: She read all of Agatha Christie’s novels one by one. One by one the guests left.
See also: by, one
Farlex Partner Idioms Dictionary

one by one

Individually in succession.
See also: by, one
American Heritage® Dictionary of the English Language, Fifth Edition.
See also:
  • cooking for one
  • drive (one) out of office
  • force (one) out of office
  • force out of office
  • except for one thing
  • give (one) (one's) head
  • give head
  • give somebody their head
  • give someone their head