Quiet alto performing for philosopher (5)
I believe the answer is:
plato
'for philosopher' is the definition.
(Plato is an example)
'quiet alto performing' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'performing' indicates an anagram.
'alto' is an anagram of 'lato'.
'p'+'lato'='PLATO'
(Other definitions for plato that I've seen before include "A plot (anag) (known to Aristotle?)" , "Ancient Greek philosopher" , "Ancient Athenian philosopher, pupil of Socrates" , "Greek philosopher, disciple of Aristotle" , "To pal up with Greek philosopher" .)