Influencing each other (11)
I believe the answer is:
interactive
'influencing each other' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for interactive that I've seen before include "Communicating with others in a group" , "(Of two things) influencing each other" , "Able to afford two-way communication" , "Sort of program" , "Showing mutual influence" .)