This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
禩 combines 示 (altar, spirit) with 異 (unusual, different). The exact historical development is uncertain, but it likely relates to a rare ritual or ancestral term.
The left side 示 suggests a ritual or spiritual context, while the right side 異 means unusual. Picture an unusual altar used for a rare ceremony, but remember the meaning itself is uncertain.
For シ, imagine a rare ritual where everyone must be silent: shhh -> シ, as the unusual ceremony begins at the altar.
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