Son given rebuke is down (4)
I believe the answer is:
swig
'is down' is the definition.
'son given rebuke' is the wordplay.
'son' becomes 's'.
'given' says to put letters next to each other.
'rebuke' becomes 'wig' (wig is a kind of rebuke).
's'+'wig'='SWIG'
(Other definitions for swig that I've seen before include "Large swallow" , "Gulp of drink" , "Drink deeply" , "Drink (a deep draught)" , "Slug" .)