Big cuddle by sweetheart (4)
I believe the answer is:
huge
'big' is the definition.
('huge' can be similar in meaning to 'big')
'cuddle by sweetheart' is the wordplay.
'cuddle' becomes 'hug' (I've seen this before).
'by' is a charade indicator (letters next to each other).
'sweetheart' becomes 'e' (the heart/centre of 'sweet'**).
'hug'+'e'='HUGE'
(Other definitions for huge that I've seen before include "Colossal" , "Unusually large" , "Mammoth" , "giant" , "Jumbo" .)