Key Italian used in authentic musical performance (7)
I believe the answer is:
recital
'musical performance' is the definition.
(thesaurus)
'key italian used in authentic' is the wordplay.
'key' becomes 'c' (I've seen this in other clues**).
'italian' becomes 'it'.
'used in' is an insertion indicator.
'authentic' becomes 'real' (I've seen this before).
'c'+'it'='cit'
'cit' inserted inside 'real' is 'RECITAL'.
(Other definitions for recital that I've seen before include "Article (anag)" , "(Usually solo) concert" , "Concert by soloist" , "One's performance" , "statement of facts" .)