French river to the English Channel (5)
I believe the answer is:
somme
'french river to the english channel' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for somme that I've seen before include "runner" , "1916 battleground" , "French river known from First World War" , "World War One battle region" , "bloody fight" .)