Insulting doctor or aged Conservative (10)
I believe the answer is:
derogatory
'insulting' is the definition.
(thesaurus)
'doctor or aged conservative' is the wordplay.
'doctor' indicates anagramming the letters.
'conservative' becomes 'tory' (I've seen this before).
'or'+'aged'='oraged'
'oraged' anagrammed gives 'deroga'.
'deroga'+'tory'='DEROGATORY'
(Other definitions for derogatory that I've seen before include "Insulting" , "Disparaging" , "Showing a disrespectful attitude" , "deliberately offensive" .)