Principal sports car, the original model (9)
I believe the answer is:
archetype
'the original model' is the definition.
(I've seen this before)
'principal sports car' is the wordplay.
'principal' becomes 'arch' (as in arch-enemy).
'sports car' becomes 'E-type' (type of Jaguar car).
'arch'+'etype'='ARCHETYPE'
(Other definitions for archetype that I've seen before include "Perfect example" , "Original, prototype" , "Original model from which others are copied" , "They caper about like original model" , "Original pattern or model" .)