Philosopher paid for a doctor (13)
I believe the answer is:
metaphysician
'philosopher' is the definition.
(thesaurus)
'paid for a doctor' is the wordplay.
'paid for' becomes 'meta' (I can't justify this - if you can you should believe this answer much more).
'a doctor' becomes 'physician' ('physician' can be a synonym of 'doctor').
'meta'+'physician'='METAPHYSICIAN'
Can you help me to learn more?
(Other definitions for metaphysician that I've seen before include "One skilled in philosophical groundworks" , "Kant, for one" .)