This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
瑫 combines 王 (jade) with 舀, which likely contributes the sound. The exact historical development is uncertain.
The left side is 王 (jade), and the right side is 舀 (a shape associated with scooping or a mortar). Picture a jade scoop, but its exact meaning is unclear.
For トウ, imagine a jade toe ring: toe -> トウ, and the jade 王 component ties it to the kanji.
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