Young man's bread from New York, maybe bagel (5)
I believe the answer is:
bucko
'bagel' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?
'young man's bread from new york' is the wordplay.
'young man' becomes 'buck' (old-fashioned term for a young man).
'bread from new york' becomes 'o' (I can't justify this - if you can you should believe this answer much more).
'buck'+'o'='BUCKO'
'maybe' is the link.
Can you help me to learn more?
(Other definitions for bucko that I've seen before include "Lively young Irish fellow" , "One swaggering" , "Young lad" , "Young Irishman" , "Fellow swaggering" .)