Effete English rogue gripped by depression (8)
I believe the answer is:
decadent
'effete' is the definition.
(synonyms)
'english rogue gripped by depression' is the wordplay.
'english' becomes 'E' (abbreviation).
'rogue' becomes 'cad' (I've seen this before).
'gripped by' indicates putting letters inside.
'depression' becomes 'dent' (dent is a kind of depression).
'e'+'cad'='ecad'
'ecad' going within 'dent' is 'DECADENT'.
(Other definitions for decadent that I've seen before include "Culturally in decline" , "Morally corrupt" , "Debauched" , "Morally deficient; declining" , "Reprobate" .)