So abandoned the son, in that case (4)
I believe the answer is:
then
'in that case' is the definition.
(synonyms)
'so abandoned the son' is the wordplay.
'abandoned' suggests deleting specific letters.
'the'+'son'='theson'
'theson' with 'so' removed is 'THEN'.
(Other definitions for then that I've seen before include "soon?" , "Consequently" , "Afterwards - as a result" , "Subsequently - previously" , "At that time; next" .)