French river report is sensible (4)
I believe the answer is:
sane
'sensible' is the definition.
(sane can mean sensible or reasonable)
'french river report' is the wordplay.
'french river' becomes 'seine' (I've seen this before).
'report' shows a homophone (sound like) (as heard, or reported by someone).
'seine' is a homophone of 'SANE'.
'is' is the link.
(Other definitions for sane that I've seen before include "In full possession of mental faculties" , "Right-minded" , "Identical" , "Compos mentis" , "Mentally sound" .)