Raced round a tree (5)
I believe the answer is:
cedar
'a tree' is the definition.
(cedar is a kind of tree)
'raced round' is the wordplay.
'round' indicates an anagram.
'raced' is an anagram of 'CEDAR'.
(Other definitions for cedar that I've seen before include "Raced around noble tree" , "Fragrant conifer" , "Raced around a mighty tree" , "Cypress-like tree" , "representative of Lebanon?" .)