noun pl. oratorios
Origin: It, lit., small chapel (< LL(Ec) oratorium: see oratory, sense ): from the performance of such compositions at the Oratory of Saint Philip Neri in Rome
See oratorio in American Heritage Dictionary 4
noun pl. or·a·to·ri·os
Origin: , after Oratorio, the Oratory of Saint Philip Neri at Rome, where famous musical services were held in the 16th century.
Learn more about oratorio