Economist with German husband supporting second president (4,5)
I believe the answer is:
adam smith
'economist' is the definition.
(18th-century economist)
'with german husband supporting second president' is the wordplay.
'with german' becomes 'mit' ('with' in German).
'husband' becomes 'h'.
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'second president' becomes 'Adams' (John Adams, second president of the USA).
'mit'+'h'='mith'
'mith' after 'adams' is 'ADAM SMITH'.
(Other definitions for adam smith that I've seen before include "Advocate of free trade" , "The Wealth of Nations author" , "Moral philosopher" , "Economist" .)