One must have to have it! (9)
I believe the answer is:
ownership
'one' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'to have it' is the wordplay.
I cannot quite see how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found in the answer.
'to have' could be 'own' (to have something is to own it) and 'own' is located in the answer.
This explanation may well be incorrect...
'must have' acts as a link.
Can you help me to learn more?
(Other definitions for ownership that I've seen before include "Legal title" , "Proprietorship, possession" , "Proprietary right of possession" , "The right of possessing something" .)