3s, for which one has permanent possession (5)
I believe the answer is:
keeps
'has permanent possession' is the definition.
'keeps' can be an answer for 'has' (keeping is a kind of having). I am not sure about the 'permanent possession' bit.
'3s for which one' is the wordplay.
I cannot quite understand how this works, but
'3s' could be 's' and 's' is found within the answer.
The remaining letters 'keep' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for keeps that I've seen before include "Stores" , "Retains" .)