Pavarotti's OK in an opera house (7)
I believe the answer is:
mansion
'house' is the definition.
(synonyms)
'pavarotti's ok in an opera' is the wordplay.
'pavarotti's ok' becomes 'si' ('yes' in Italian - eg for Pavarotti).
'in' means one lot of letters goes inside another.
'an opera' becomes 'manon' (Jules Massenet opera).
'si' placed inside 'manon' is 'MANSION'.
(Other definitions for mansion that I've seen before include "Handsome house as for Lord Mayor" , "Manor house" , "Grand house" , "housing" , "Large house" .)