Force to take two Frenchmen in exchange (8)
I believe the answer is:
commerce
'exchange' is the definition.
(thesaurus)
'force to take two frenchmen in' is the wordplay.
'two frenchmen' means two replacements for 'frenchman'.
'force' becomes 'coerce' (synonyms).
'to take' indicates putting letters inside (inserted letters are taken in).
'frenchman' becomes 'M' (abbreviation for Monsieur - like 'Mr').
'frenchman' becomes 'M' (abbreviation for Monsieur - like 'Mr').
'in' indicates putting letters inside.
'coerce' enclosing 'm' is 'comerce'.
'comerce' going around 'm' is 'COMMERCE'.
(Other definitions for commerce that I've seen before include "Business, industry, trade" , "Transactions in goods and services" , "Business dealings" , "The buying and selling of commodities and services" , "Sales and purchases of goods and services" .)