Retirement allowance? Not artificial, but extraordinary (12)
I believe the answer is:
supernatural
'extraordinary' is the definition.
(thesaurus)
'retirement allowance? not artificial' is the wordplay.
'retirement allowance?' becomes 'super' (I can't explain this - if you can you should give a lot more credence to this answer).
'not artificial' becomes 'natural' ('natural' is the opposite to 'artificial').
'super'+'natural'='SUPERNATURAL'
'but' is the link.
Can you help me to learn more?
(Other definitions for supernatural that I've seen before include "Magic" , "Not of this world" , "Magical; occult" , "unknown to science" , "Miraculous, magical" .)