This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
椉 is an older or variant form of 乗 (ride, board). The exact historical development of its components is uncertain.
The top 亠 looks like a lid or cover, and the bottom 桀 suggests a wooden structure. Picture a covered wooden palanquin or cart that you ride on.
For ショウ, imagine a showy ride: show -> ショウ, and you are riding in a decorated vehicle.