ケイ, おさか, ぎょう
punish, penalty, sentence, punishment
JLPT1 G7 S6 F864
The relevant oracle bone form of 开# is a depiction of handcuffs stretching about a prisoner's wrists, framing them in punishment. A bronzeware inscription form curves the vertical strokes. 刑 adds 刀 sword/knife → *punish* (by confinement, severing of body parts or by other means).
[Full Kanji Etymology List]