This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 弫 is uncertain. It combines 弓 (bow) with 臣, but the original semantic or phonetic role of 臣 in this character is unclear.
A bow 弓 beside a minister 臣 suggests a strong bow, but the meaning is uncertain.
For シン, imagine a strong bow that makes a sharp 'shin' sound when released: shin -> シン.