Cuckoo's home by French river reportedly (6)
I believe the answer is:
insane
'cuckoo's' is the definition.
(thesaurus)
'home by french river reportedly' is the wordplay.
'home' becomes 'in' ('he's home' can mean 'he's in').
'by' is a charade indicator (letters next to each other).
'french river' becomes 'seine' (I've seen this before).
'reportedly' shows a homophone (sound like).
'seine' sounds like 'sane'.
'in'+'sane'='INSANE'
(Other definitions for insane that I've seen before include "Quite mad" , "Deranged, crazy" , "Mad, irrational" , "Harebrained" , "Mentally ill" .)