fat, corpulent
膃 centers on excess flesh: being fat or corpulent. It describes a body state of plumpness or obesity.
膃 combines the flesh radical ⺼ with a phonetic component that includes 囚 and 皿. The right side likely contributes the sound オツ, while the flesh radical indicates the meaning relates to the body. The exact historical development of the right-side component is uncertain.
The left side ⺼ is flesh, and the right side looks like a person trapped (囚) over a plate (皿). Imagine someone who is so fat they are trapped in their own flesh, sitting over a plate of food.
For オツ, imagine an obese person trying to fit into a small space and making a strained sound: 'Ots!' The sound オツ matches the effort of carrying excess flesh.