A spirit of the garden (4)
I believe the answer is:
arum
'the garden' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'a spirit' is the wordplay.
'spirit' becomes 'rum' (alcoholic spirit).
'a'+'rum'='ARUM'
'of' is the link.
Can you help me to learn more?
(Other definitions for arum that I've seen before include "Plant with small flowers and arrow-shaped leaves - kind of lily" , "Perennial" , "Plant like cuckoo pint" , "plant with a white spathe" , "A spirit for a lily" .)