San'indō

is a Japanese term denoting both an ancient division of the country, corresponding for the most part with the modern conception of the San'in region, and the main road running through it. San'in translates to "the shaded side of a mountain", while dō, depending on the context, can mean either a road, or a circuit, in the sense of delineating a region. This name derives from the idea that the northern side of the central mountain chain running through Honshū was the "shaded" side, while the southern side was the "sunny" (山陽 San'yō) side.
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