reins
羇 centers on the idea of reins used to control or guide a horse. Its meaning is narrow and concrete, referring specifically to the straps held by a rider.
The exact historical development of 羇 is uncertain. It visually contains 罒 (net) and a lower component related to leather (革), which may suggest reins made of leather straps, but this is speculative.
The top 罒 looks like a net or mesh, and the bottom 䩭 contains 革 (leather). Picture a leather net-like harness used as reins to guide a horse.
For キ, imagine holding the reins tightly and saying 'key' because the reins are the key to controlling the horse: key -> キ.