Reveller in some wild orgy taking ecstasy (9)
I believe the answer is:
partygoer
'reveller' is the definition.
(a reveller is someone who parties)
'some wild orgy taking ecstasy' is the wordplay.
'some' becomes 'part' (only part of something).
'wild' indicates anagramming the letters.
'taking' means one lot of letters goes inside another.
'ecstasy' becomes 'E' (informal term for the drug).
'orgy' is an anagram of 'ygor'.
'ygor' going around 'e' is 'ygoer'.
'part'+'ygoer'='PARTYGOER'
'in' acts as a link.
(Other definitions for partygoer that I've seen before include "One raving perhaps" , "One who celebrates" .)