Tree by an old barn appearing black initially (6)
I believe the answer is:
baobab
'tree' is the definition.
(baobab is a kind of tree)
'by an old barn appearing black initially' is the wordplay.
'initially' says to take the initial letters.
The initial letters of 'by an old barn appearing black' is 'BAOBAB'.
(Other definitions for baobab that I've seen before include "Growth seen in Africa" , "Tree indigenous to Africa and Australia" , "Exotic tree" , "Gigantic tropical tree with very thick trunk" , "Monkey-bread tree" .)