mountain in Gansu province
峒 is a rare kanji that refers specifically to a mountain in Gansu province. Its meaning is a proper geographic name rather than a general concept.
峒 combines 山 (mountain) with 同, which likely provides the sound. It is a phono-semantic compound used for a specific place name.
The left side is 山 (mountain) and the right side is 同 (same). Picture a mountain in Gansu that looks the same from every angle, making it easy to identify as 峒.
For トウ, imagine a tall mountain peak shaped like a toe: toe -> トウ, and that toe-shaped peak is the mountain in Gansu.
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