Rough diamonds in French street (4)
I believe the answer is:
rude
'rough' is the definition.
(similar in meaning)
'diamonds in french street' is the wordplay.
'diamonds' becomes 'd' (abbreviation in bridge say).
'in' means one lot of letters goes inside another.
'french street' becomes 'rue' (French for street or road).
'd' going within 'rue' is 'RUDE'.
(Other definitions for rude that I've seen before include "lacking refinement" , "Uncivil" , "'Bad-mannered, discourteous (4)'" , "Insolent" , "Unpleasant" .)