This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
垟 combines 土 (earth) with 羊 (sheep), but the exact historical development and original meaning are uncertain.
The left side is earth 土 and the right side is a sheep 羊. Picture a sheep standing on a patch of earth, but the meaning of this kanji remains unclear.
For ヨウ, imagine a sheep 羊 on the earth 土 saying 'yo!' to greet you: yo -> ヨウ.
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