Weaken understanding (10)
I believe the answer is:
compromise
This clue is a double definition.
'weaken' is the first definition.
(I know that weaken can be written as compromise)
'understanding' is the second definition.
(I know that compromise is a type of settlement)
(Other definitions for compromise that I've seen before include "Middle course" , "Settlement" , "accommodation" , "Settle by concession" , "Trade-off" .)