A king left around northern part of France (7)
I believe the answer is:
argonne
'part of france' is the definition.
('Argonne' is part of 'france')
'a king left around northern' is the wordplay.
I cannot really understand how this works, but
'a' is within the answer.
'king' could be 'r' (abbreviation of Latin rex) and 'r' is found in the answer.
'around' could be 'o' (a round letter) and 'o' is found within the answer.
'northern' could be 'n' (abbreviation e.g. N. Ireland) and 'n' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for argonne that I've seen is " Forested area of First World War".)