French flower? Sounds reasonable (5)
I believe the answer is:
seine
'french flower?' is the definition.
(I've seen this in another clue)
'sounds reasonable' is the wordplay.
'sounds' indicates a 'sounds like' (homophone) clue.
'reasonable' becomes 'sane' (similar in meaning).
'sane' is a homophone of 'SEINE'.
(Other definitions for seine that I've seen before include "Parisian river" , "Second longest river in France" , "French river -- type of fishing net" , "Paris river" , "Paris's river" .)