The French ship carries a smaller amount (4)
I believe the answer is:
less
'a smaller amount' is the definition.
(I've seen this in another clue)
'the french ship carries' is the wordplay.
'the french' becomes 'le' ('the' in French).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'carries' is a charade indicator (letters next to each other) (in a down clue, some letters go beneath others).
'le'+'ss'='LESS'
(Other definitions for less that I've seen before include "inferior" , "Smaller in amout or degree" , "A smaller amount" , "So-called St James" , "more, as they say" .)