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late 14c., "sea monster, sea serpent," also regarded as a form of Satan, from Late Latin leviathan, from Hebrew livyathan "dragon, serpent, huge sea animal," of unknown origin, perhaps related to liwyah "wreath," from root l-w-h- "to wind, turn, twist." Of powerful persons or things from c.1600. Hobbes's use is from 1651.
a transliterated Hebrew word (livyathan), meaning "twisted," "coiled." In Job 3:8, Revised Version, and marg. of Authorized Version, it denotes the dragon which, according to Eastern tradition, is an enemy of light; in 41:1 the crocodile is meant; in Ps. 104:26 it "denotes any large animal that moves by writhing or wriggling the body, the whale, the monsters of the deep." This word is also used figuratively for a cruel enemy, as some think "the Egyptian host, crushed by the divine power, and cast on the shores of the Red Sea" (Ps. 74:14). As used in Isa. 27:1, "leviathan the piercing [R.V. 'swift'] serpent, even leviathan that crooked [R.V. marg. 'winding'] serpent," the word may probably denote the two empires, the Assyrian and the Babylonian.