Walnut or apple (4)
I believe the answer is:
tree
This clue is a double definition.
'walnut' is the first definition.
(thesaurus)
'apple' is the second definition.
(thesaurus)
(Other definitions for tree that I've seen before include "Plant with a main trunk and branches" , "Large, woody perennial plant" , "Sequoia, for example" , "Tall wooden plant" , "plane, say?" .)