Insist Parisian's very charming quality comes back (6)
I believe the answer is:
assert
'insist' is the definition.
(asserting is a kind of insisting)
'parisian's very charming quality comes back' is the wordplay.
'parisian's very' becomes 'tres' (I've seen this in another clue).
'charming quality' becomes 'sa' (I am not sure about this - if you are sure you should believe this answer much more).
'comes back' says the letters should be written backwards.
'tres'+'sa'='tressa'
'tressa' backwards is 'ASSERT'.
Can you help me to learn more?
(Other definitions for assert that I've seen before include "Maintain - allege" , "State authoritatively" , "protest" , "State firmly and with conviction" , "Establish control or state as true" .)