Dilute or weaken (5,4)
I believe the answer is:
water down
I believe this is a double definition.
'dilute' is the first definition.
(I know that water down is a kind of dilute)
'weaken' is the second definition.
(I know that water down is a kind of cut)
(Other definitions for water down that I've seen before include "Lessen impact" , "Dilute by adding H20" , "Dilute - make less controversial" , "Dilute, make less forceful or vivid" .)