Ointment mark on light wood (6)
I believe the answer is:
balsam
'ointment' is the definition.
(I know that balsam is a type of ointment)
'mark on light wood' is the wordplay.
'mark' becomes 'm'.
'on' is a charade indicator (letters next to each other).
'light wood' becomes 'balsa' (I've seen this before).
'm' after 'balsa' is 'BALSAM'.
(Other definitions for balsam that I've seen before include "Fragrant resin used in medicine and perfumes" , "Herb for healing" , "flowering plant" , "Resin-yielding tree" , "Soothing herb" .)