Stave character (4)
I believe the answer is:
'stave character' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for clef that I've seen before include "Sign of (musical) pitch" , "Symbol on a stave to show the pitch" , "Treble or bass on a stave" , "Musical notation on a staff" , "Item of musical notation" .)