let down, suspend, hand, down
埀 centers on the action of letting something hang or be suspended downward, and by extension handing something down or lowering it.
埀 is a variant form of 垂, which historically depicts something hanging down. The exact development of the variant shape is uncertain.
The top part looks like something hanging from above, and the lower part resembles a hand or support letting it down. Picture a hand lowering a suspended object.
For スイ, imagine a swing being let down from a tree: swing -> スイ, and the rope is suspended downward.