French dish with water that's flat (7)
I believe the answer is:
plateau
'flat' is the definition.
(thesaurus)
'french dish with water' is the wordplay.
'french dish' becomes 'plat' (I can't explain this - if you can you should give a lot more credence to this answer).
'with' is a charade indicator (letters next to each other).
'water' becomes 'eau' (I have seen 'French water ' mean 'eau' so perhaps 'water' could also mean 'eau').
'plat'+'eau'='PLATEAU'
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for plateau that I've seen before include "Raised level area" , "Large level tract of elevated land" , "Flat raised land" , "Flat-topped upland" , "one has no inclination" .)