This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
阦 combines the mound radical ⻖ with 火 (fire). The exact historical development is uncertain, and no clear meaning is recorded.
The left side is a mound or hill, and the right side is fire. Picture a fire burning on a hill, but the kanji's meaning remains unclear.
For ヨウ, imagine a yo-yo on fire rolling down the mound: yo-yo -> ヨウ, and the fire burns on the hill.