become emaciated
膄 centers on the body wasting away: becoming thin, emaciated, or physically diminished.
膄 combines the flesh component ⺼ with 叟, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with physical wasting.
The flesh radical ⺼ on the left suggests the body, and 叟 looks like a thin, hunched figure. Picture a person whose flesh has wasted away, leaving them emaciated.
For シュウ, imagine a person becoming so thin that their clothes look like a loose shoe: shoe -> シュウ, and the body inside is emaciated.