Make mournful (6)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
sadden
'make mournful' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sadden that I've seen before include "Cause to feel unhappy" , "Make mournful" , "get down" , "Make melancholy and distressed" , "Dismay" .)