Bumpy in the heart of cobbled street (12)
I believe the answer is:
thoroughfare
'street' is the definition.
(I know that thoroughfare is a type of street)
'bumpy in the heart of cobbled' is the wordplay.
'bumpy' becomes 'rough' (similar in meaning).
'in' means one lot of letters goes inside another.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'heart' becomes 'h' (card game abbreviation).
'cobbled' becomes 'are' (I can't explain this - if you can you should give a lot more credence to this answer).
't'+'h'+'of'='thof'
'rough' inserted inside 'thof' is 'thoroughf'.
'thoroughf'+'are'='THOROUGHFARE'
Can you help me to learn more?
(Other definitions for thoroughfare that I've seen before include "Access - road" , "Public way or street" , "Road or path" , "Main road" , "Public road" .)