Long tree (4)
I believe the answer is:
pine
This clue is a double definition.
'long' is the first definition.
(to pine for someone is to long for them)
'tree' is the second definition.
(pine is a kind of tree)
(Other definitions for pine that I've seen before include "Evergreen conifer" , "Long - timber" , "Long - tree" , "A tree to grieve for" , "Tree, waste away" .)