dust
坱 centers on fine, airborne particles: dust. It refers to the loose, powdery material that settles on surfaces or hangs in the air.
坱 combines 土 (earth, soil) with 央, which likely contributes the sound. The character is used to represent dust or fine particles of earth.
The left side is 土 (earth), and the right side 央 looks like a person with a wide stance. Imagine a person stomping on dry earth, kicking up a cloud of dust.
For オウ, picture an old owl shaking dust from its feathers: owl -> オウ, and the dust flies off the earth.