Throw line into water by the French chateaux (7)
I believe the answer is:
castles
'water by the french chateaux' is the definition.
I can't tell whether this definition defines the answer.
'throw line into' is the wordplay.
'throw' becomes 'cast' (synonyms).
'line' becomes 'l' (used when specifying particular lines from a poem).
'into' becomes 'es' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'cast'+'l'+'es'='CASTLES'
Can you help me to learn more?
(Other definitions for castles that I've seen before include "Keeps" , "Don't build the chess pieces in the air" , "buildings" , "pieces for chess board" , "Forts" .)