This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
盨 is a rare character. It visually combines 須 and 皿, but the exact historical development is uncertain.
The top 須 suggests something needed, and the bottom 皿 is a dish. Imagine a special dish needed for a ritual, but its exact purpose is unclear.
For シュ, picture a shoe (シュ) placed on the dish 皿 as an offering: shoe -> シュ, and the dish holds the needed item.