... high part in vocal tonally (4)
I believe the answer is:
alto
'high' is the definition.
(similar in meaning)
'part in vocal tonally' is the wordplay.
'part in' indicates a hidden word.
'ALTO' is hidden in the letters of 'vocal tonally'.
(Other definitions for alto that I've seen before include "High male singing voice" , "A singing voice or pitch" , "Kind of singing voice, male or female" , "Highest male voice: lowest female voice" , "Second of four parts (in singing)" .)