A retiring habit (10)
I believe the answer is:
nightdress
'a retiring habit' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'retiring habit' is the wordplay.
'retiring' becomes 'night' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'habit' becomes 'dress' (I've seen this in another clue).
'night'+'dress'='NIGHTDRESS'
Can you help me to learn more?
(Other definitions for nightdress that I've seen before include "item of bedwear" , "Sleeping attire" .)