This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 緃 is uncertain. It appears to combine 糸 (thread) with a right-side component that may be related to 从 or 從, but the original meaning and component function are unclear.
The left side 糸 suggests thread or fabric. The right side looks like a person 人 over a stop 止, but without a clear meaning, picture a mysterious thread pattern that is hard to interpret.
For ショウ, imagine showing (ショウ) someone this rare thread pattern, but they just shrug because its meaning is unclear: show -> ショウ.