Go round the bend endlessly in French department (4)
I believe the answer is:
orne
'french department' is the definition.
(I've seen this in another clue)
'go round the bend endlessly' is the wordplay.
'go' becomes 'one' (I can't explain this - if you can you should believe this answer much more).
'round' is an insertion indicator.
'the bend' becomes 'arc' (arc can mean to curve or bend).
'endlessly' means to look at the middle letters (the ends of the words are removed).
The centre of 'arc' is 'r'.
'one' enclosing 'r' is 'ORNE'.
'in' is the link.
Can you help me to learn more?
(Another definition for orne that I've seen is " part of France".)