Learned borrowing from Ancient Greek χάος (kháos, “vast chasm, void”). Doublet of gas, which was borrowed through Dutch. In Early Modern English, used in the sense of the original Greek word. In the meaning "primordial matter" from the 16th century. Figurative usage in the sense "confusion, disorder" from the 17th century. The technical sense in mathematics and science dates from the 1960s.