Big cuddle on Ecstasy! (4)
I believe the answer is:
huge
'big' is the definition.
('huge' can be similar in meaning to 'big')
'cuddle on ecstasy' is the wordplay.
'cuddle' becomes 'hug' (I've seen this before).
'on' means one lot of letters go next to another.
'ecstasy' becomes 'e' (informal term for the drug).
'hug'+'e'='HUGE'
(Other definitions for huge that I've seen before include "Unusually large" , "Massive" , "Extremely large" , "giant" , "Jumbo" .)