Beat Adam's son soundly (4)
I believe the answer is:
cane
'beat' is the definition.
(caning is a kind of beating)
'adam's son soundly' is the wordplay.
'adam's son' becomes 'cain' (I've seen this before).
'soundly' shows a homophone (sound like).
'cain' sounds like 'CANE'.
(Other definitions for cane that I've seen before include "Rod for beating" , "Bamboo rod" , "Slender stem of bamboo etc" , "Punish; woody stem" , "Flog" .)