"Republic" philosopher (5)
I believe the answer is:
plato
'republic philosopher' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for plato that I've seen before include "Greek character" , "Teacher of Aristotle, pupil of Socrates" , "Republic author" , "A plot (anag) (known to Aristotle?)" , "Ancient Greek philosopher" .)