Macron, perhaps, rejected help to get attacker (9)
I believe the answer is:
diacritic
'macron perhaps' is the definition.
(macron is a kind of diacritic)
'rejected help to get attacker' is the wordplay.
'rejected' says the letters should be written in reverse.
'help' becomes 'aid' (synonyms).
'to get attacker' becomes 'critic' (I can't justify this - if you can you should give a lot more credence to this answer).
'aid' backwards is 'dia'.
'dia'+'critic'='DIACRITIC'
Can you help me to learn more?
(Other definitions for diacritic that I've seen before include "grave perhaps" , "accent, for example" , "one showing a pronounced difference" , "Mark" , "[ACCENT] , perhaps" .)