Start rewriting notes (5)
I believe the answer is:
onset
'start' is the definition.
(onset is a kind of start)
'rewriting notes' is the wordplay.
'rewriting' is an anagram indicator.
'notes' anagrammed gives 'ONSET'.
(Other definitions for onset that I've seen before include "Initial stage; attack" , "origin" , "Assault; beginning" , "Kick-off" , "Start - opening moments" .)