Hollowed-out wood in tree is coarse (5)
I believe the answer is:
bawdy
'coarse' is the definition.
(I've seen this before)
'hollowed-out wood in tree' is the wordplay.
'hollowed out' says to hollow out the word (remove centre letters).
'in' is an insertion indicator.
'tree' becomes 'bay' (bay is a kind of tree).
'wood' with its centre taken out is 'wd'.
'wd' inserted within 'bay' is 'BAWDY'.
'is' acts as a link.
(Other definitions for bawdy that I've seen before include "Humorously obscene" , "Humorously indecent" , "Ribald" , "Blue" , "coarse" .)