hiding enclosure radical (no. 23)
匸 is a radical that represents a hiding enclosure or a box that conceals something. Its standalone meaning is tied to this idea of covering or hiding.
匸 is a pictograph of a box or enclosure with a lid, representing the idea of hiding or covering. The exact historical development is uncertain, but the shape clearly suggests a container.
The shape looks like a box with a lid that extends to one side, hiding whatever is inside. Think of a secret compartment that conceals its contents.
For ケイ, imagine a hidden key inside the enclosure: key -> ケイ, and the box hides the key.