Artificial part of expert’s argument (10)
I believe the answer is:
prosthesis
'artificial part' is the definition.
'expert's argument' is the wordplay.
'expert's' becomes 'pros'.
'argument' becomes 'thesis' (I've seen this before).
'pros'+'thesis'='PROSTHESIS'
'of' is the link.
(Other definitions for prosthesis that I've seen before include "Artificial body-part" , "False part" , "This may supply missing part" , "what can help a handicapped person" , "artificial substitute" .)