tall bamboo
篔 refers specifically to a type of tall bamboo. The meaning is narrow and concrete, without broader abstract extensions.
篔 combines 竹 (bamboo) with 員, which likely contributes the sound. The character was created to name a specific tall bamboo species.
The top 竹 is bamboo, and the bottom 員 looks like a round container. Imagine a bamboo so tall it reaches the clouds, with its round sections stacked high.
For ウン, picture a tall bamboo swaying in the wind, making an 'oon' sound as it bends: oon -> ウン.