Yearn for tree (4)
I believe the answer is:
pine
I believe this is a double definition.
'yearn' is the first definition.
('pine' can be a synonym of 'yearn')
'tree' is the second definition.
(pine is a kind of tree)
'for' acts as a link.
(Other definitions for pine that I've seen before include "type of wood" , "Coniferous tree" , "Yearn for evergreen tree" , "Long - tree" , "Long - timber" .)