This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 愑 is uncertain. It combines 忄 (heart) with 勇, but the original semantic and phonetic roles are unclear.
The heart radical 忄 beside 勇 suggests a brave or emotional heart, but the actual meaning is uncertain.
For ヨウ, imagine a brave heart shouting 'Yo!' as it charges forward: Yo -> ヨウ, and the heart 忄 is full of courage 勇.