Notice republican prophet (4)
I believe the answer is:
seer
'prophet' is the definition.
(both can mean someone who tells the future)
'notice republican' is the wordplay.
'notice' becomes 'see' (notice can mean to spot or see).
'republican' becomes 'r' (abbreviation).
'see'+'r'='SEER'
(Other definitions for seer that I've seen before include "One divines the future" , "Prophet or visionary" , "Sage with 20ac" , "One fortelling future" , "Sibyl" .)