Something that represents the sound of a percussion instrument (6)
I believe the answer is:
symbol
'something that represents' is the definition.
I can't tell whether this definition defines the answer.
'sound of a percussion instrument' is the wordplay.
'sound of' shows a homophone (sound like).
'a percussion instrument' becomes 'cymbal' (cymbal is a kind of percussion instrument).
'cymbal' sounds like 'SYMBOL'.
'the' is the link.
Can you help me to learn more?
(Other definitions for symbol that I've seen before include "Something representative" , "Material object representing something abstract" , "Emblem, representation" , "Meaningful character" , "It represents or suggests something else" .)