Spring in Raynes Park (3)
I believe the answer is:
spa
'spring' is the definition.
(thesaurus)
'in raynes park' is the wordplay.
'in' indicates the answer is hidden within the clue.
'SPA' is hidden within 'raynes park'.
(Other definitions for spa that I've seen before include "Bath, possibly" , "A curative mineral spring, or place with one" , "well" , "health centre" , "Curative resort" .)