Conceal the south-east Greek island (7)
I believe the answer is:
secrete
'conceal' is the definition.
(I've seen this in another clue)
'the south-east greek island' is the wordplay.
'the south east' becomes 'SE' (abbreviation).
'greek island' becomes 'crete' (Crete is a Greek island).
'se'+'crete'='SECRETE'
(Other definitions for secrete that I've seen before include "Hide away" , "Hide; as gland does" , "Hide - discharge" , "Place out of sight, hide" , "Hide or conceal an object" .)