Frenchman and Scotsman are in a state (9)
I believe the answer is:
louisiana
'a state' is the definition.
(Louisiana is an example)
'frenchman and scotsman are' is the wordplay.
'frenchman' becomes 'louis' (I can't explain this - if you can you should give a lot more credence to this answer).
'and' is a charade indicator (letters next to each other).
'scotsman' becomes 'ian' (common Scottish name).
'are' becomes 'a' (short for 'are', historical unit of measurement).
'louis'+'ian'+'a'='LOUISIANA'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for louisiana that I've seen before include "State named for French king" , "IOU a snail over in the US state" , "that's near Mississippi" , "US state, capital Baton Rouge" , "Southern United State on the Gulf of Mexico" .)