Narrowly defeat Greek character, quiet (3)
I believe the answer is:
pip
'narrowly defeat' is the definition.
(I've seen this before)
'greek character quiet' is the wordplay.
'greek character' becomes 'pi' (letter from the Greek alphabet).
'quiet' becomes 'p' (music symbol for 'piano').
'pi'+'p'='PIP'
(Other definitions for pip that I've seen before include "star" , "Small fruit seed" , "Dickens hero" , "Greenwich time signal" , "Just defeat; apple seed" .)