chaos (n.)

late 14c., "gaping void; empty, immeasurable space," from Old French chaos (14c.) or directly from Latin chaos, from Greek khaos "abyss, that which gapes wide open, that which is vast and empty," from *khnwos, from PIE root *ghieh- "to yawn, gape, be wide open."

Meaning "utter confusion" (c. 1600) is an extended sense from theological use of chaos in the Vulgate version of "Genesis" (1530s in English) for "the void at the beginning of creation, the confused, formless, elementary state of the universe." The Greek for "disorder" was tarakhe, but the use of chaos here was rooted in Hesiod ("Theogony"), who describes khaos as the primeval emptiness of the Universe, and in Ovid ("Metamorphoses"), who opposes Khaos to Kosmos, "the ordered Universe." Sometimes it was personified as a god, begetter of Erebus and Nyx ("Night").

Meaning "orderless confusion" in human affairs is from c. 1600. Chaos theory in the modern mathematical sense is attested from c. 1977.

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Definitions of chaos from WordNet
chaos (n.)
a state of extreme confusion and disorder;
Synonyms: pandemonium / bedlam / topsy-turvydom / topsy-turvyness
chaos (n.)
the formless and disordered state of matter before the creation of the cosmos;
chaos (n.)
(physics) a dynamical system that is extremely sensitive to its initial conditions;
Chaos (n.)
(Greek mythology) the most ancient of gods; the personification of the infinity of space preceding creation of the universe;