Robin has a sash for his middle (3)
I believe the answer is:
'a sash for his middle' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'robin has' is the wordplay.
'has' indicates the answer is hidden within the clue.
'OBI' is hidden within 'robin'.
Can you help me to learn more?
(Other definitions for obi that I've seen before include "Broad Japanese sash" , "Long cloth" , "Spells" , "Martial arts sash" , "sash from Tokyo" .)