This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 榺 is uncertain. It visually contains 木 (tree) inside a structure resembling 勝 without 力, but the original component relationships are unclear.
Since the meaning is unclear, focus on the shape: a tree 木 trapped inside a complex enclosure. Imagine a rare, mysterious tree hidden within an ancient structure.
For ショウ, picture a show (ショウ) being performed around the hidden tree inside 榺: the show reveals the tree's secret.