Singer appearing in festival today (4)
I believe the answer is:
alto
'singer' is the definition.
(alto is a kind of singer)
'in festival today' is the wordplay.
'in' says the answer is hidden in the clue.
'ALTO' is hidden within 'festival today'.
'appearing' acts as a link.
(Other definitions for alto that I've seen before include "Lowest female singing voice" , "someone to sing" , "The highest adult male singing-voice" , "Member of choir" , "Singing voice between tenor and soprano" .)