Stash in home counties island (7)
I believe the answer is:
secrete
'stash' is the definition.
(thesaurus)
'home counties island' is the wordplay.
'home counties' becomes 'SE' (Home Counties in the South East of England).
'island' becomes 'Crete' (Greek island).
'se'+'crete'='SECRETE'
'in' is the link.
(Other definitions for secrete that I've seen before include "(Of gland) produce (a substance)" , "Release bodily fluid" , "Cache" , "squirrel" , "Hold and send out substance into the body as gland does" .)