This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
綗 combines 糸 (thread) with 冏, but the historical origin and original meaning are uncertain.
With 糸 (thread) on the left, 綗 might relate to textiles, but without a clear meaning it is best remembered as a rare thread-related shape.
For ケイ, imagine a rare thread being pulled straight like a cable: cable -> ケイ, and the thread 糸 is drawn taut.