oak
櫧 centers on a specific type of tree: the oak. Its meaning is narrow and concrete, referring to the oak tree itself.
櫧 combines 木 (tree) with 諸, which likely contributes the sound. The character was created to name the oak tree.
The tree radical 木 stands beside 諸, a shape that suggests many words. Picture an oak tree with many leaves, each leaf a word, making it the 'word tree' — an oak.
For ショ, imagine a short oak tree: short -> ショ, and the oak is a short, sturdy tree.