This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
愶 combines 忄 (heart) with 脅, which likely contributes the sound. The exact historical development is uncertain.
The heart radical 忄 beside 脅 suggests a feeling of being threatened or coerced, but the exact meaning is unclear.
For キョウ, imagine a heart (忄) being threatened (脅) by a loud 'kyou' sound: kyou -> キョウ.