On which a caged bird would long to be? (4)
I believe the answer is:
pine
'be?' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for pine that I've seen before include "Long - timber" , "type of wood" , "A tree to grieve for" , "Mope; tree" , "Conifer grown for wood" .)