The Hebrew verb kavah means to burn, scorch, or sear, particularly the burning that leaves a mark or wound. It refers to the kind of painful burning experienced in judgment or suffering.
The root kavah is used in Proverbs 6:28 in a wisdom comparison about the inescapability of sin's consequences — can one walk on hot coals without his feet being scorched? The word graphically illustrates how sin burns those who engage it. It also connects to the concept of God's refining fire, which purges but also has consequences for the unrepentant.