Adopted boy stamps down thus (7)
I believe the answer is:
stepson
'stamps down thus' is the definition.
I can't judge whether this definition defines the answer.
'adopted boy' is the wordplay.
'adopted' becomes 'step' (I can't justify this - if you can you should believe this answer much more).
'boy' becomes 'Son' (synonyms).
'step'+'son'='STEPSON'
Can you help me to learn more?
(Other definitions for stepson that I've seen before include "Spouse's child from previous marriage" , "could be issue for partner" , "Tramples (5,2) -- relative" , "Male child of spouse by earlier marriage" , "boy not sharing blood" .)