Make Black Sea magical (7)
I believe the answer is:
charmed
'magical' is the definition.
(thesaurus)
'make black sea' is the wordplay.
'make black' becomes 'char' (to char is to blacken by burning).
'sea' becomes 'med' (short for Mediterranean).
'char'+'med'='CHARMED'
(Other definitions for charmed that I've seen before include "Entranced" , "Unusually lucky" , "Enchanted" , "blessed by fortune" .)