The French going to one river hideaway (4)
I believe the answer is:
lair
'hideaway' is the definition.
(thesaurus)
'the french going to one river' is the wordplay.
'the french' becomes 'la' (**).
'going to' is a charade indicator (letters next to each other).
'one' becomes 'i' (Roman numeral).
'river' becomes 'r'.
'la'+'i'+'r'='LAIR'
(Other definitions for lair that I've seen before include "office?" , "Rail around animal's den" , "Place to hide" , "Hideaway, den" , "Habitation of a wild animal" .)