Approve going round a tree (3)
I believe the answer is:
oak
'tree' is the definition.
(oak is a type of tree)
'approve going round a' is the wordplay.
'approve' becomes 'ok' (synonyms).
'going round' means one lot of letters goes inside another (some letters go around others).
'ok' placed around 'a' is 'OAK'.
(Other definitions for oak that I've seen before include "Building timber" , "Common forest tree" , "Its seed is the acorn" , "Nose of certain wines" , "Traditional British tree" .)