fence, hedge, wall
牆 centers on a physical barrier that encloses or divides space: a wall, fence, or hedge. All given meanings are concrete boundary structures.
牆 combines 爿 (a split wood or bed component) with 嗇, which likely contributes the sound. The character is associated with walls and enclosures, but the exact historical development of the components is uncertain.
The left side 爿 looks like a wooden frame, and the right side 嗇 contains 口 (enclosure) and 土 (earth). Picture a wooden-framed earthen wall or fence enclosing a space.
For ショウ, imagine a show being performed behind a tall fence: show -> ショウ, and the wall hides the stage.