Four taking part in erotic feast (8)
I believe the answer is:
carnival
'feast' is the definition.
(carnival is a kind of feast)
'four taking part in erotic' is the wordplay.
'four' becomes 'iv' (roman numeral).
'taking part in' means one lot of letters goes inside another.
'erotic' becomes 'carnal' (I've seen this before).
'iv' placed into 'carnal' is 'CARNIVAL'.
(Other definitions for carnival that I've seen before include "Dvorak overture" , "Time of public revelry" , "travelling fair" , "Period of public revelry" , "Public celebration with processions, music, etc" .)