Son gets syrup drink (4)
I believe the answer is:
swig
'drink' is the definition.
(swig is a kind of drink)
'son gets syrup' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'gets' says to put letters next to each other.
'syrup' becomes 'wig' ('syrup of fig' is Cockney rhyming slang for 'wig').
's'+'wig'='SWIG'
(Other definitions for swig that I've seen before include "Drink deeply" , "Large swallow" , "Drink in large draughts" , "Large gulp from the bottle" , "(Take) quick drink from bottle" .)