A Parisian's help not declared (6)
I believe the answer is:
unsaid
'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).
'uns'+'aid'='UNSAID'
(Other definitions for unsaid that I've seen before include "left to the imagination" , "withdrawn" , "with lack of expression" , "Not uttered" , "not stated?" .)