There are several synonyms that can be used to describe an opera with a rural theme. One such word is pastoral, which suggests an idyllic countryside setting and a focus on nature and simple joys. Another word that could be used is bucolic, which connotes a rustic and rural atmosphere. A third option is agrarian, which suggests a focus on agricultural life and the land. Other synonyms could include rustic, countryside, or even agricultural. Ultimately, the choice of synonym depends on the specific qualities of the opera in question. However, regardless of the word used, any rural-themed opera is likely to evoke a sense of nostalgia and reflect on life in simpler times.