This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
敐 combines 辰 and 攵, but the exact historical development is uncertain. It may be a phono-semantic compound, but the original meaning is unclear.
The left side 辰 suggests a morning or dragon, and the right side 攵 suggests an action. Without a clear meaning, imagine a dragon stirring at dawn, moving joyfully.
For シン, imagine the dragon's joyful movement making a shimmering sound: shin -> シン.