Whittle down (4)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
pare
'whittle down' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pare that I've seen before include "Cut down gradually" , "Strip the skin from" , "Whittle" , "Trim off in layers" , "Shave or peel" .)