Lower-class ruffian retreats, having stolen my French gown (6)
I believe the answer is:
kimono
'gown' is the definition.
(I have seen 'Oriental gown' mean 'kimono' so perhaps 'gown' could also mean 'kimono')
'lower-class ruffian retreats having stolen my french' is the wordplay.
I cannot quite see how this works, but
'my french' could be 'mon' ('my' in French) and 'mon' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for kimono that I've seen before include "Japanese attireimoni" , "Loose robe, originally Japanese" , "Japanese dress" , "dressing-gown" , "Traditional Japanese robe with wide sleeves" .)