Inferior school shut (7)
I believe the answer is:
schlock
'inferior' is the definition.
Both the definition and answer are singular nouns.
Perhaps you can see an association between them that I can't see?
'school shut' is the wordplay.
'school' becomes 'sch' (common abbreviation).
'shut' becomes 'lock' (I can't justify this - if you can you should give a lot more credence to this answer).
'sch'+'lock'='SCHLOCK'
Can you help me to learn more?
(Another definition for schlock that I've seen is " Trashy (Yiddish)".)