cut, slice off, pierce
刲 centers on cutting with a blade: slicing off, piercing, or cutting into something.
刲 combines 圭 (possibly a phonetic component) with 刂 (knife), suggesting a cutting action. The exact historical development is uncertain.
The left side 圭 looks like stacked earth, and the right side 刂 is a knife. Imagine a knife slicing through layered earth, cutting cleanly.
For ケイ, picture a sharp knife cutting a piece of cake: cake -> ケイ, and the knife slices it neatly.