Old, stout businessman (8)
I believe the answer is:
exporter
'businessman' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'old stout' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'stout' becomes 'porter' (synonyms).
'ex'+'porter'='EXPORTER'
Can you help me to learn more?
(Other definitions for exporter that I've seen before include "One making foreign sales" , "one sells abroad" , "trading abroad" , "one selling overseas" , "One selling abroad" .)