Molière has one to help upcoming reviewer (9)
I believe the answer is:
diacritic
'moliere has one' is the definition.
('Molire' is spelled with a diacritic)
'help upcoming reviewer' is the wordplay.
'help' becomes 'aid' ('aid' can be a synonym of 'help').
'upcoming' is a reversal indicator.
'reviewer' becomes 'critic' (I've seen this before).
'aid' written backwards gives 'dia'.
'dia'+'critic'='DIACRITIC'
'to' is the link.
(Other definitions for diacritic that I've seen before include "one showing a pronounced difference" , "grave perhaps" , "[ACCENT] , perhaps" , "Capable of distinguishing" , "accent, for example" .)