A stocking X for Oz inventor (4)
I believe the answer is:
baum
'oz inventor' is the definition.
The definition suggests a singular noun which matches the answer.
'a stocking x' is the wordplay.
I cannot really understand how this works, but
'a' is within the answer.
The remaining letters 'bum' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'for' acts as a link.
Can you help me to learn more?
(Another definition for baum that I've seen is " L Frank -, Wizard of Oz writer".)