Duke ingesting MDMA joins a celebration (6)
I believe the answer is:
fiesta
'celebration' is the definition.
(fiesta is a kind of celebration)
'duke ingesting mdma joins a' is the wordplay.
'duke' becomes 'fist' (put up your dukes).
'ingesting' is an insertion indicator.
'mdma' becomes 'E' (MDMA is ecstasy, ie 'E').
'joins' says to put letters next to each other.
'fist' going around 'e' is 'fiest'.
'fiest'+'a'='FIESTA'
(Other definitions for fiesta that I've seen before include "Spanish holiday" , "Latin American celebration" , "(Spanish) religious festival" , "celebration abroad" , "Feast day" .)