Trade in timber (4)
I believe the answer is:
deal
I believe this clue is a double definition.
'trade in' is the first definition.
(thesaurus)
'timber' is the second definition.
(deal is a kind of timber)
(Other definitions for deal that I've seen before include "Buy and sell" , "split deck" , "Agreement; hand out cards" , "Sawn wood" , "A port; a (good) amount" .)