to toss about, to swing, to rock
蘯 centers on unsteady, back-and-forth motion: tossing about, swinging, or rocking. The meanings all describe something being moved loosely or agitated.
蘯 is a phono-semantic compound with 艹 (grass) and 盪, which likely provides both sound and the idea of washing or shaking. The exact historical development is uncertain.
Grass 艹 on top of 盪, a shape associated with washing or shaking. Picture grass being tossed and swung around in a washing basin, rocking back and forth.
For トウ, imagine a toe caught in the grass, making you swing and rock to free it: toe -> トウ.