small box, chest, casket
匭 centers on a container for storing or securing items: a small box, chest, or casket.
匭 combines the enclosure 匚 (box) with 軌 (track, rut), likely suggesting a container with a defined shape or function. The exact historical development is uncertain.
The outer 匚 is a box, and inside is 軌 (track). Imagine a small box with tracks or grooves inside, like a chest with compartments for keeping things organized.
For キ, picture a small box that holds a key: key -> キ. The key unlocks the chest.