This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
璱 combines 王 (jade) with 瑟, which likely contributes the sound. The exact historical development is uncertain.
The jade radical 王 suggests a connection to precious stones, but the overall meaning is unclear. Picture a mysterious jade artifact whose purpose is unknown.
For シツ, imagine a sheet of jade: sheet -> シツ, though the meaning remains uncertain.