Utter in semitones (4)
I believe the answer is:
emit
'utter' is the definition.
(synonyms)
'in semitones' is the wordplay.
'in' indicates the answer is hidden within the clue.
'EMIT' is hidden in the letters of 'semitones'.
(Other definitions for emit that I've seen before include "Discharge - utter" , "Give off, gas say" , "Send out in time" , "'Give off, odour say (4)'" , "Exhale" .)