This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 夨 is uncertain. It visually contains 大 with an additional stroke, but its origin and original meaning are unclear.
Since the meaning is unclear, focus on the shape: 夨 looks like a person (大) with a small mark above, perhaps tilting or leaning.
For ショク, imagine a shockingly rare kanji: shock -> ショク, and this strange 夨 shape is a shock to see.