To make something with a hole, push the middle out fully - just the middle (5)
I believe the answer is:
bagel
'middle' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for bagel that I've seen before include "Hard doughnut-shaped roll" , "Ring-shaped bread product" , "Jewish baked roll" , "Ring-shaped bread roll" , "Doughnut-shaped bread roll" .)