The Hebrew verb zud means to boil over, to act insolently or presumptuously, to behave arrogantly. The image is of a pot boiling over — uncontrolled pride that overflows its proper bounds. It can also mean to boil food, but its moral usage dominates the theological vocabulary.
In the Torah, zud describes the gravest form of willful sin — the presumptuous transgressor who acts in deliberate defiance against God. Deuteronomy 17:12-13 mandates death for the person who 'presumes' to disobey the priest or judge. This contrasts sharply with sins of ignorance (which could be atoned by sacrifice). The concept underlies Psalm 19:13's plea: 'Keep your servant also from presumptuous sins.' The New Testament equivalent is seen in warnings about 'willful sin' after receiving the knowledge of truth (Hebrews 10:26). The image of boiling over is apt: pride left unchecked inevitably overflows into rebellion against God.