Conceal in a south-east Greek island (7)
I believe the answer is:
secrete
'conceal' is the definition.
(I know that secrete is a kind of conceal)
'south-east greek island' is the wordplay.
'south east' becomes 'SE' (abbreviation).
'greek island' becomes 'crete' (Crete is a Greek island).
'se'+'crete'='SECRETE'
'in a' is the link.
(Other definitions for secrete that I've seen before include "Release bodily fluid" , "Place out of sight, hide" , "Cache" , "(Of gland) produce (a substance)" , "squirrel" .)