ends of bow
弰 centers on the tips or ends of a bow, the curved extremities where the bowstring is attached.
弰 combines 弓 (bow) with 肖, which likely contributes the sound and may relate to the idea of a tip or end. The exact historical development is uncertain.
The left side is a bow 弓, and the right side 肖 looks like a small pointed tip. Picture the curved ends of a bow where the string is tied.
For ソウ, imagine the sound of a bowstring being released: 'sou' — the ends of the bow vibrate with a 'sou' sound.