French nobleman failing to keep order, ending in defeat (7)
I believe the answer is:
vicomte
'french nobleman' is the definition.
(I've seen this before)
'failing to keep order ending in defeat' is the wordplay.
'failing' becomes 'vice' (vice can mean a moral failing).
'to keep' means one lot of letters goes inside another.
'order' becomes 'om' (Order of Merit).
'ending in' suggests the final letters.
The final letter of 'defeat' is 't'.
'om'+'t'='omt'
'vice' enclosing 'omt' is 'VICOMTE'.
(Other definitions for vicomte that I've seen before include "Foreign nobleman" , "French nobleman" , "Noble" .)