Fell — drop (3,4)
I believe the answer is:
cut down
I believe this clue is a double definition.
'fell' is the first definition.
(I've seen this before)
'drop' is the second definition.
(synonyms)
(Other definitions for cut down that I've seen before include "Felled" , "Fell a tree or reduce usage as in a diet" , "Reduce the length of" , "Economise or despatch with sword" .)