This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The historical origin of 甧 is uncertain. It visually combines 甡 (doubled 生) with 月, but the component relationship is unclear.
The kanji has no clear meaning, but visually it shows doubled life (生) over a moon (月). This could suggest abundance or multiplicity, but treat any meaning as speculative.
For シン, imagine a scene of abundant life under the moon: a shin (シン) bone from a feast of plenty, tying the reading to the visual shape.