This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 兓 is uncertain. It visually consists of two 兂 components, but the origin and original meaning are unclear.
Two identical shapes side by side, but no clear meaning emerges. Think of it as a mysterious double symbol.
For シン, imagine two identical shapes shin-ing faintly in the dark: shin -> シン, though the meaning remains hidden.