Man that's engaged to be shown round northern capital (7)
I believe the answer is:
finance
'capital' is the definition.
(thesaurus)
'man that's engaged to be shown round northern' is the wordplay.
'man that's engaged' becomes 'fiance' (someone engaged to be married).
'to be shown round' means one lot of letters goes inside another.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'fiance' enclosing 'n' is 'FINANCE'.
(Other definitions for finance that I've seen before include "Money management" , "funding" , "Supply funds" , "See 9" , "Provide capital" .)