This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development is uncertain. The modern form visually combines the food radical 飠 with the phonetic component 主, but no clear historical origin is available.
The left side 飠 suggests food, and the right side 主 looks like a master or lord. Picture a master chef preparing a special dish, but the exact meaning is unclear.
For シュ, imagine a master chef saying 'shoo!' as he waves away a fly from the food: shoo -> シュ.
deep-fried mochi (Heian period)