horse chestnut
橡 centers on the horse chestnut tree and its nuts. The meaning is specific to that tree species.
橡 combines 木 (tree) with 象, which likely contributes the sound. The character was created to name the horse chestnut tree.
The tree radical 木 beside 象 (elephant) suggests a tree with large, elephant-ear-like leaves or big nuts, like a horse chestnut.
For ショウ, imagine a horse chestnut tree putting on a show of large leaves and spiky nuts: show -> ショウ.