The primary Hebrew word for "holy," derived from qadash, meaning "to be set apart." Holiness is the defining attribute of God — His utter uniqueness, separation from all that is common, and moral perfection. When applied to people, places, or objects, it means they have been dedicated to God's purposes.
The triple declaration "Holy, holy, holy" in Isaiah 6:3 is the only divine attribute repeated three times — emphasizing that holiness qualifies all other attributes. God's love is holy love; God's justice is holy justice. The call to "be holy, for I am holy" (Leviticus 19:2) is the call to reflect God's character in every area of life.
Rudolf Otto's The Idea of the Holy describes God's holiness as mysterium tremendum et fascinans — a mystery that simultaneously terrifies and attracts. The holiness code in Leviticus 17–26 shows practical implications for all of life. The Greek hagios (G40) carries this into the New Testament.