Sanction or advocate (7)
I believe the answer is:
endorse
This clue is a double definition.
'sanction' is the first definition.
(I know that endorse is a more specific form of sanction)
'advocate' is the second definition.
(I've seen this before)
(Other definitions for endorse that I've seen before include "Back, sanction" , "Uphold" , "Ratify" , "Approve or underwrite" , "Add one's authority to" .)