vague, dim, twilight
曨 centers on dim, unclear light: the vague, hazy quality of twilight when shapes lose their sharpness.
曨 combines 日 (sun) with 龍, likely as a phonetic component, to express dim or hazy light. The exact historical development is uncertain.
The sun 日 is wrapped in the misty coils of a dragon 龍, making the light vague and dim like twilight.
For ロウ, picture a low, dim sun barely visible through dragon-shaped mist: low -> ロウ, and the light is vague.