Promenade protecting island garden (8)
I believe the answer is:
paradise
'garden' is the definition.
(I've seen this before)
'promenade protecting island' is the wordplay.
'promenade' becomes 'parade' (synonyms).
'protecting' means one lot of letters goes inside another (inserted letters are held or protected).
'island' becomes 'is' (abbreviation).
'parade' enclosing 'is' is 'PARADISE'.
(Other definitions for paradise that I've seen before include "Felicity" , "Scene of bliss" , "one enjoyed before the fall" , "Poem by 1" , "Place of utter bliss" .)