This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
諈 combines 言 (speech) with 垂, which likely contributes the sound. The exact historical development is uncertain.
With 言 (speech) beside 垂, imagine words hanging down like a pendant, but the meaning is unclear.
For スイ, picture a swing (スイ) made of words hanging from the 垂 component: swing -> スイ.