Ecstasy consequently found in endless modern rave (7)
I believe the answer is:
enthuse
'rave' is the definition.
(I've seen this before)
'ecstasy consequently found in endless modern' is the wordplay.
'ecstasy' becomes 'e' (informal term for the drug).
'consequently' becomes 'thus' (I've seen this before**).
'found in' means one lot of letters goes inside another.
'endless' means to remove the last letter.
'modern' becomes 'neo' ('neo' can be similar in meaning to 'modern').
'neo' with its final letter removed is 'ne'.
'thus' put within 'ne' is 'nthuse'.
'e'+'nthuse'='ENTHUSE'
(Other definitions for enthuse that I've seen before include "Show feeling of eager liking and approval" , "Show passionate zeal (about something)" , "Gush in praise" , "Cheer" , "Inspire with keenness" .)