sickness, repeated
殗 is a rare kanji whose given meanings are 'sickness' and 'repeated'. The connection between these two ideas is unclear, and the kanji has no clear standalone conceptual center. Treat its meaning as uncertain.
殗 combines 歹 (death/sickness) with 奄, which may contribute a phonetic element. The exact historical development is uncertain, and the modern form is rare.
The left side 歹 suggests death or sickness, and the right side 奄 looks like a person under a roof. Picture a sick person confined indoors, and the sickness keeps returning repeatedly.
For ヨウ, imagine a sick person weakly saying 'yo' as they call for help: 'yo' -> ヨウ, and the sickness keeps coming back.