Vast abuse of cocaine (7)
I believe the answer is:
oceanic
'vast' is the definition.
(synonyms)
'abuse of cocaine' is the wordplay.
'abuse of' indicates an anagram (I've seen 'abuse' mean this).
'cocaine' with letters rearranged gives 'OCEANIC'.
(Other definitions for oceanic that I've seen before include "Like the main" , "Relating to large seas" , "description of rollers" , "Of the open sea" , "vast waves?" .)