Faithful model on the Parisian street (4)
I believe the answer is:
true
'faithful' is the definition.
(synonyms)
'model on the parisian street' is the wordplay.
'model' becomes 't' (Ford Model T car).
'on' means one lot of letters go next to another.
'the parisian street' becomes 'rue' ('street' in French).
't'+'rue'='TRUE'
(Other definitions for true that I've seen before include "Straight or loyal" , "Real; loyal" , "Honest and straight" , "In accordance with fact" , "Unwavering" .)