wooden rammer, wooden pestle, place
檇 centers on a heavy wooden tool used for pounding or crushing: a wooden rammer or pestle. The place-name sense is a specific application, likely from a location associated with such a tool or a similar shape.
檇 combines 木 (tree/wood) with 雋, which likely contributes the sound and may relate to the idea of pounding or a pointed tool. The exact historical development is uncertain.
The left side 木 is wood, and the right side 雋 looks like a heavy tool with a bird-like top and a sturdy base. Picture a wooden pestle made from a tree trunk, ready to pound grain.
For スイ, imagine swinging the wooden rammer in a smooth arc: swing -> スイ, and the heavy wood comes down with a thud.