French one left Italian in the dark (5)
I believe the answer is:
unlit
'in the dark' is the definition.
(I've seen this before)
'french one left italian' is the wordplay.
'french one' becomes 'un' ('one' in French).
'left' becomes 'l' (common abbreviation).
'italian' becomes 'it' (abbreviation for Italian).
'un'+'l'+'it'='UNLIT'
(Other definitions for unlit that I've seen before include "dim" , "not provided with a lamp?" , "With no lighting" , "such as dark alley?" , "Left in the dark" .)