Shut up Italian writer at street festival (9)
I believe the answer is:
pentecost
'festival' is the definition.
(I've seen this before)
'shut up italian writer at street' is the wordplay.
'shut up' becomes 'pent' (synonyms).
'italian writer' becomes 'Eco' (Umberto Eco, p9ne-e0p6).
'at' is a charade indicator (letters next to each other).
'street' becomes 'st' (abbreviation).
'pent'+'eco'+'st'='PENTECOST'
(Other definitions for pentecost that I've seen before include "Christian festival on Whit Sunday" , "Whitsuntide" .)