Good wood flanks new grate (5)
I believe the answer is:
gnash
'grate' is the definition.
(gnashing is a kind of grating)
'good wood flanks new' is the wordplay.
'good' becomes 'g' (abbreviation).
'wood' becomes 'ash' (ash is a kind of wood).
'flanks' means one lot of letters goes inside another (flank can mean to go on either side of).
'new' becomes 'n'.
'g'+'ash'='gash'
'gash' enclosing 'n' is 'GNASH'.
(Other definitions for gnash that I've seen before include "Hangs (anag.)" , "Grind away" , "Grind (teeth) together" , "champ" , "Grind one's teeth" .)