cover, shelter, screen, protect
幪 centers on covering or sheltering something to protect it, like a screen or cloth that shields from view or harm.
幪 combines 巾 (cloth) with 蒙, which likely contributes the sound and the idea of covering or enveloping. The exact historical development of 蒙 is uncertain.
The left side 巾 is a cloth, and the right side 蒙 looks like something being wrapped or covered. Imagine a large cloth draped over an object to shelter and protect it.
For ボウ, picture a bow (ボウ) made of cloth that you use to cover and protect a gift: bow -> ボウ.