king-post
栭 refers to a king-post, a vertical structural post in traditional roof framing. The meaning is a single, specific architectural term.
栭 combines 木 (tree/wood) with 而, which likely contributes the sound. The exact historical development is uncertain, but the character is used for a wooden architectural element.
The left side 木 is wood, and the right side 而 looks like a post with a crossbeam. Picture a wooden king-post standing upright in a roof frame.
For ジ, imagine a king-post made of wood that looks like the letter G: G -> ジ, and the post supports the roof.