The schoolkids wouldn’t miss him (3)
I believe the answer is:
sir
'the schoolkids wouldn't miss him' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'him' is the wordplay.
I cannot really understand how this works, but
'him' could be 'si' and 'si' is found in the answer.
A single letter 'r' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sir that I've seen before include "Polite term of address for a man" , "Polite or formal address to male" , "Formal term of address" , "Male form of address" , "Way to address gentleman" .)