This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
裑 combines the clothing radical 衤 with 身 (body). The exact historical development is uncertain, but it likely relates to clothing for the body.
The left side is clothing 衤, and the right side is body 身. Picture a garment fitted to the body, but its exact meaning is unclear.
For シン, imagine a thin shin being measured for a custom garment: shin -> シン, and the clothing wraps around the body.