Term used by the KJV to translate two closely related Hebrew words (tannim and tannin). At times the terms appear to be interchangeable. Context indicates that the first term refers to a mammal inhabiting the desert (Isa 13:22; 35:7; 43:20; Lam 4:3). Most modern speech translation equate the animal with the jackal, though perhaps the wolf (REB) is intended. The second term has four possible uses: (1) “great sea monster” (KJV, “great whales”) in the sense of a large sea
creature (Gen 1:21; Psa 149:7), possibly a whale; this sense of tannin as created being may serve as a correction of sense 4; (2) a snake (Exod 7:9-10; Deut 32:33; Psa 91:13); (3) a crocodile (Jer 51:34; Ezek 29:3; 32:3); here the beast is used as a symbol of Nebuchadnezzar of Babylon or the Egyptian Pharaoh; (4) a mythological sea monster symbolic of the forces of chaos and evil in opposition of God’s creative and redemptive work (Psa 74:12-14; Job 7:12; 26:12-13; Isa 27:1; 51:9-10). Leviathan and Rehab are used as parallel terms.
In the NT Revelation develops sense 4, describing the dragon as a great, red monster with seven heads and ten horns. This dragon is clearly identified with Satan (the Devil) and is termed the deceiver and the accuser of the saints. As in the OT texts, the dragon is put under guard (Rev 20:3; Job 7:12) and later released for final destruction (Rev 20:7-10; Isa 27:1).