Dads drink on Sunday (4)
I believe the answer is:
pops
'dads' is the definition.
('pop' can be a synonym of 'dad')
'drink on sunday' is the wordplay.
'drink' becomes 'pop' (pop is a kind of drink).
'on' is a charade indicator (letters next to each other).
'sunday' becomes 's'.
'pop'+'s'='POPS'
(Other definitions for pops that I've seen before include "light classical pieces" , "Explodes, bursts" , "Dads or sweet drinks" , "Bursts noisily" .)