Good wood cut (4)
I believe the answer is:
gash
'cut' is the definition.
(I've seen this before)
'good wood' is the wordplay.
'good' becomes 'g' (abbreviation).
'wood' becomes 'ash' (I've seen this before).
'g'+'ash'='GASH'
(Other definitions for gash that I've seen before include "Wide cut" , "injury" , "score heavily" , "Cut; waste (colloq.)" , "surplus to requirements" .)