A Parisian's help not declared (6)
I believe the answer is:
'not declared' is the definition.
(not declared or said)
'a parisian's help' is the wordplay.
'a parisian's' becomes 'un's' ('a' in French).
'help' becomes 'aid' (synonyms).
(Other definitions for unsaid that I've seen before include "left to the imagination" , "withdrawn" , "with lack of expression" , "Not uttered" , "not stated?" .)