to step, stride equal to half a pace
跬 centers on a measured step: specifically, a stride equal to half a pace. The broader idea is stepping or taking a step.
跬 combines 足 (foot) with 圭, which likely contributes the sound. The character expresses a step or stride measured by the foot.
The left side 足 means foot, and the right side 圭 looks like stacked earth. Imagine a foot stepping over small mounds of earth, each step exactly half a pace.
For キ, picture a key step: you need the right key to unlock the next half-pace stride. Key -> キ, and your foot takes that measured step.