Marine's cocaine supply (7)
I believe the answer is:
oceanic
'marine's' is the definition.
(marine means relating to the sea)
'cocaine supply' is the wordplay.
'supply' indicates an anagram (in a supple way).
'cocaine' is an anagram of 'OCEANIC'.
(Other definitions for oceanic that I've seen before include "Relating to great seas" , "Relating to large areas of sea" , "Cocaine (anag)" , "Relating to large seas" , "overwhelming" .)