Rural, rustic, pastoral, bucolic are comparable when they mean of or characteristic of the country as distinguished from city life.
Rural is the most comprehensive term; in its widest meaning it implies open country whether uninhabited or sparsely settled; more narrowly it suggests agricultural pursuits or simple community life. In distinction from rustic, however, rural suggests the pleasant aspects of country life; rustic commonly implies a contrast with the refinements of the city or the town and often connotes rudeness or lack of polish.
Pastoral and bucolic derive some or most of their connotations from the literary treatment of rural life.
Pastoral, when it does not refer directly to the life of shepherds, suggests either green pastures and grazing sheep or a life primitive in its simplicity or idyllic in its peace and apartness from the world.
Bucolic, a curiously dichotomous word, may be a close synonym of pastoral in stressing the charm of rural environment and life or may come close to rustic in emphasizing the crudity and lack of refinement of rural life or people.