cover
幭 centers on the idea of a covering, especially a cloth or fabric cover. The single given meaning 'cover' is the core concept.
幭 combines 巾 (cloth) with 蔑, which likely provides the sound. The character is rare, and its exact historical development is uncertain.
The left side 巾 is a cloth, and the right side 蔑 looks like a complex object being covered. Imagine draping a cloth over something to cover it completely.
For ベツ, imagine covering a bed with a cloth: bed -> ベツ, and the cloth covers it.