International Standard Bible Encyclopedia (1915)
(liwyathan (Job 41:1-34), from [~lawah, "to fold"; compare Arabic name of the wry neck, Iynx torquilla, abu-luwa, from kindred lawa, "to bend"):
(1) The word "leviathan" also occurs in Isa 27:1, where it is characterized as "the swift serpent .... the crooked serpent"; in Ps 104:26, where a marine monster is indicated; also in Ps 74:14 and Job 3:8. The description in Job 41 has been thought by some to refer to the whale, but while the whale suits better the expressions denoting great strength, the words apply best on the whole to the crocodile. Moreover, the whale is very seldom found in the Mediterranean, while the crocodile is abundant in the Nile, and has been known to occur in at least one river of Palestine, the Zarqa, North of Jaffa. For a discussion of the behemoth and leviathan as mythical creatures, see EB, under the word "Behemoth" and "Leviathan." The points in the description which may well apply to the crocodile are the great invulnerability, the strong and close scales, the limbs and the teeth. It must be admitted that there are many expressions which a modern scientist would not use with reference to the crocodile, but the Book of Job is neither modern nor scientific, but poetical and ancient.
(2) See Astronomy, sec. II, 2, 5.