reject, abandon, discard
弃 centers on the act of throwing something away or leaving it behind: rejecting, abandoning, or discarding.
弃 is the modern simplified form of 棄. The older form combines a pictograph of a child being abandoned with two hands, expressing rejection or discarding. The modern form retains the top 亠 and a simplified lower shape.
The top 亠 looks like a lid, and the bottom 弁 suggests hands holding something. Picture putting a lid on unwanted items and using both hands to throw them away: 弃 means reject or discard.
For キ, imagine a key being thrown away because it no longer fits: key -> キ, and the act of discarding the key matches the meaning of 弃.