Uncouth number seen in French street (4)
I believe the answer is:
rude
'uncouth' is the definition.
('rude' can be a synonym of 'uncouth')
'number seen in french street' is the wordplay.
'number' becomes 'd' (D is an example**).
'seen in' indicates putting letters inside.
'french street' becomes 'rue' (French for street or road).
'd' going inside 'rue' is 'RUDE'.
(Other definitions for rude that I've seen before include "dirty" , "Base" , "Lacking civility" , "Blue" , "Uncivilised" .)