shuttle
梭 centers on a shuttle, the tool that carries thread back and forth in weaving. The meaning is concrete and specific to that object.
梭 combines 木 (wood) with 夋, which likely contributes the sound and may relate to movement or passing. The character originally referred to a wooden shuttle used in weaving.
The left side is 木 (tree/wood), and the right side 夋 looks like a shuttle moving back and forth with its angular strokes. Picture a wooden shuttle flying through the loom.
For サ, imagine a shuttle sawing back and forth through the threads: saw -> サ, and the wooden shuttle moves like a saw.