This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 脋 is uncertain. It visually contains 刕 (a tripled knife component) over 月 (flesh/meat), but the original semantic and phonetic roles are unclear.
The kanji has no clear meaning, but visually it looks like three knives (刕) over flesh (月), which could suggest cutting or threatening, though this is only a visual guess.
For キョウ, imagine a threatening scene with three knives over flesh, and someone shouts 'KYOU!' (today) in alarm: 今日 (きょう) -> キョウ, tying the reading to the visual shape.