This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
瑢 combines 王 (jade) with 容, which likely contributes the sound. The exact historical development is uncertain.
The left side 王 suggests jade or a precious stone, and the right side 容 suggests a container or form. Picture a jade vessel, but the exact meaning is uncertain.
For ヨウ, imagine a jade vessel being used to hold a yo-yo: yo -> ヨウ, and the jade container holds the toy.
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