After good promotion buy appliance (6)
I believe the answer is:
gadget
'appliance' is the definition.
(synonyms)
'after good promotion buy' is the wordplay.
'after' means one lot of letters go next to another.
'good' becomes 'g' (abbreviation).
'promotion' becomes 'ad' (ad is a kind of promotion).
'buy' becomes 'get' (both can mean to purchase or obtain).
'g' put next to 'ad' is 'gad'.
'gad'+'get'='GADGET'
(Other definitions for gadget that I've seen before include "Small mechanical device or tool" , "Useful small device" , "Clever device" , "Gizmo, contraption" , "Gismo" .)