in turn—
1. one at a time in sequence; one after the other:
- He asked each of the boys in turn whether they had taken the book.
2. (also: in one’s turn) when one’s turn or opportunity comes:
- I took Sally out to lunch, and she took me out in turn.
3. (of two or more people) do smth. alternating at regular intervals:
- A team of volunteers take it in turn to look after preschool children.
in turns —(also: by turns) = in turn 3:
- The boys will take it in turns to row for some estimated four days.