P at the Parthenon (3)
I believe the answer is:
rho
'p at the parthenon' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rho that I've seen before include "Gr. letter written as P" , "Greek character" , "Greek P" , "Seventeenth letter of the Greek alphabet" , "17th Greek letter" .)