Outstanding, a Parisian apartment I secured (6)
I believe the answer is:
unpaid
'outstanding' is the definition.
(similar in meaning)
'a parisian apartment i secured' is the wordplay.
'a parisian' becomes 'un'.
'apartment' becomes 'pad' (I can't explain this - if you can you should give a lot more credence to this answer).
'secured' is an insertion indicator.
'pad' enclosing 'i' is 'paid'.
'un'+'paid'='UNPAID'
Can you help me to learn more?
(Other definitions for unpaid that I've seen before include "Still owing" , "Of bill, outstanding" , "Outstanding, owing" , "Without wages" , "volunteer" .)