cover up, curtain
幬 centers on a covering that conceals or encloses: a curtain or something used to cover up.
幬 combines 巾 (cloth) with 壽, which likely provides the sound and may relate to covering or enclosing. The exact historical development is uncertain.
The cloth radical 巾 on the left suggests fabric, while the right side 壽 looks like a complex enclosure. Imagine a heavy curtain draped over a frame, covering everything behind it.
For チュウ, picture a curtain that you chew on to keep your mouth covered: chew -> チュウ, and the curtain covers you up.