Cut deeply into good wood (4)
I believe the answer is:
gash
'cut deeply' 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'
'into' is the link.
(Other definitions for gash that I've seen before include "Open wound" , "extra" , "Deep open cut" , "Long deep wound" , "Wide cut" .)