Rumor, to a rumor mill (5)
I believe the answer is:
grist
'rumor to a rumor mill' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for grist that I've seen before include "Corn to be ground" , "may be put through the mill" , "Six for grinding" , "what miller needs" , "Corn for processing" .)