Society with argument against adopting one heir (5)
I believe the answer is:
scion
'heir' is the definition.
(I've seen this before)
'society with argument against adopting one' is the wordplay.
'society' becomes 's' (common abbreviation in names of organisations).
'with' means one lot of letters go next to another.
'argument against' becomes 'con' (I've seen this in other clues).
'adopting' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'con' enclosing 'i' is 'cion'.
's'+'cion'='SCION'
(Other definitions for scion that I've seen before include "Coins (anag)" , "one of a long line" , "Young child" , "Descendant - heir" , "Descendent - heir" .)