Place in a mutual relationship (9)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
correlate
(Other definitions for correlate that I've seen before include "Make a connection between (things)" , "Bring (things) into correspondence" , "Be complementary" , "To be linked to each other; trace role (anag.)" , "Establish a mutual relationship between (things)" .)