Some troublemaker on the train in France (5)
I believe the answer is:
metro
'france' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'some troublemaker on the train' is the wordplay.
'some' says to take the centre.
'troublemaker' becomes 'imp' (little devil).
'on' is an insertion indicator (as in clothing 'on' a person).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'train' becomes 'ero' (I can't explain this - if you can you should give a lot more credence to this answer).
The middle of 'imp' is 'm'.
't' placed inside 'ero' is 'etro'.
'm'+'etro'='METRO'
'in' is the link.
Can you help me to learn more?
(Other definitions for metro that I've seen before include "Parisian rail system" , "what moves many Parisians" , "Parisian underground system" , "The Paris Underground transport system" , "Parisian underground railway" .)