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 Psalm 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" (Psalm 74:14). As used in Isaiah 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.

Noah Webster's New International Dictionary of the English Language

1. (n.) A large aquatic animal or vessel; a whale; a sea monster; an aquatic animal, described in the book of Job, ch. xli., and mentioned in other passages of Scripture.

2. (n.) The whale, or a great whale.