Son, plump and squat (6)
I believe the answer is:
stubby
'squat' is the definition.
('stubby' can be a synonym of 'squat')
'son plump' is the wordplay.
'son' becomes 's'.
'plump' becomes 'tubby' (I've seen this before).
's'+'tubby'='STUBBY'
'and' is the link.
(Other definitions for stubby that I've seen before include "Short, thick and strong" , "Thickset" , "Squat" , "Short and blunt" .)