Ecstasy within completely horrific symbolism (8)
I believe the answer is:
allegory
'symbolism' is the definition.
(thesaurus)
'ecstasy within completely horrific' is the wordplay.
'ecstasy' becomes 'e' (informal term for the drug).
'within' means one lot of letters goes inside another.
'completely' becomes 'all' (synonyms).
'horrific' becomes 'gory' (I've seen this before).
'all'+'gory'='allgory'
'e' placed inside 'allgory' is 'ALLEGORY'.
(Other definitions for allegory that I've seen before include "tale with hidden meaning" , "Its characters are personifications" , "'Gulliver's Travels', for example" , "Visible symbol of an abstract idea" , "Pilgrim's Progress, say" .)