To go so fast will aggrieve the French (6)
I believe the answer is:
hurtle
'to go' is the definition.
(hurtling is a kind of going)
'will aggrieve the french' is the wordplay.
'will' is a charade indicator (letters next to each other) (I've seen this in other clues).
'aggrieve' becomes 'hurt' (I've seen this in another clue).
'the french' becomes 'le' ('the' in French).
'hurt' put next to 'le' is 'HURTLE'.
'so fast' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for hurtle that I've seen before include "Career (along)" , "Move fast; rhymes with marine reptile" , "Rush headlong" , "Move rapidly or fall headlong" , "Rush violently" .)