Student of Socrates (5)
I believe the answer is:
plato
'student of socrates' 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 "Republic author" , "Greek philosopher (The Republic)" , "Ancient Greek philosopher" , "Moon crater named after Greek philosopher" , "Ancient Athenian philosopher, pupil of Socrates" .)