Use an ax on (3)
I believe the answer is:
hew
'use an ax on' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hew that I've seen before include "Shape wood, as with an axe" , "Carve with axe" , "Chop; sounds like colour" , "Chop or cut with axe" , "Chop (wood)" .)