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This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
儬 combines 亻 (person) with 靚, which likely contributes the sound. The exact historical development and original meaning are uncertain.
Since the meaning is unclear, focus on the shape: a person 亻 beside 靚, a character associated with quiet or ornament. Picture a person quietly decorating something.
For シン, imagine a person 亻 quietly decorating a shin (シン) guard: shin -> シン, and the person works in silence.