Sorry to the French for street with foul gas leak (6)
I believe the answer is:
rueful
'sorry' is the definition.
(synonyms)
'the french for street with foul gas leak' is the wordplay.
'the french' becomes 'f' (abbreviation).
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'street' becomes 'rue' (I have seen 'French street ' mean 'rue' so perhaps 'street' could also mean 'rue').
'with foul gas leak' becomes 'ul' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'f' put after 'rue' is 'ruef'.
'ruef'+'ul'='RUEFUL'
'to' is the link.
Can you help me to learn more?
(Other definitions for rueful that I've seen before include "Feeling remorse" , "Feeling good-humoured regret" , "Penitent" , "Showing good-humoured regret" , "Expressing wry regret" .)