P-shaped Greek letter (3)
I believe the answer is:
rho
'p-shaped greek letter' 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 "letter to Athens" , "Greek letter used as symbol for density" , "Greek letter R" , "Gr. letter written as P" , "Sophocles character" .)