Enormous junk in attic (7)
I believe the answer is:
titanic
'enormous' is the definition.
(thesaurus)
'junk in attic' is the wordplay.
'junk' is an anagram indicator.
'in'+'attic'='inattic'
'inattic' anagrammed gives 'TITANIC'.
(Other definitions for titanic that I've seen before include "Exceptionally powerful" , "Twenty one [SHIP]" , "In attic (anag.)" , "Colossal, liner" , "made of metal" .)