Philosopher bumped into a medical practitioner (13)
I believe the answer is:
metaphysician
'philosopher' is the definition.
(thesaurus)
'bumped into a medical practitioner' is the wordplay.
'bumped into' becomes 'met' (I've seen this before).
'medical practitioner' becomes 'physician' (physician is a kind of medical practitioner).
'met'+'a'+'physician'='METAPHYSICIAN'
(Other definitions for metaphysician that I've seen before include "One skilled in philosophical groundworks" , "Kant, for one" .)