Leviathan: Strong's Hebrew index, #3882; livyathan=liv-yaw-thawn--(from #3867; lavah=law-vaw--to twine or twist to unite) A wreathed [twisted] animal, a large sea monster.
Job 41:1-10
God says to Job, Can you draw out Leviathan with a fish-hook? [No.] Or press down his tongue with a cord? [No.] Can you put a rope in his nose? [No.] Or pierce his jaw with a hook? [No.] Will he make many supplications to you? [No, he won't beg.] Or will he speak to you soft words? [No.] Will he make a covenant with you? [No, no agreements.] Will you take him for a servant forever? [Not a chance.] Will you play with him as with a bird? [Hardly.] Or will you bind him for your maidens? [A plaything for your little girls?] Will the traders bargain over him? [No] Will they divide him among the merchants? [Cut him up? With what knife?] Can you fill his skin with harpoons, or his head with fishing spears? [Nothing could penetrate.] Lay your hand on him; remember the battle; you will not do it again! [If you survive, you'll never attempt it again!] Behold your expectation is false [if you think you can survive an encounter with him]; will you be laid low even at the sight of him? [Just being close enough to see him!] No one is so fierce that he dares to arouse him [no living human being.]
So God tells Job that this sea-monster cannot be caught or tamed or merchandised. No hook, no harpoon, no spear would be able to penetrate his skin. God made this dragon to be impervious to any man's attempt to subdue him.
Psalm 74:13-14
Thou didst divide the sea by Thy strength; Thou didst break the heads of the sea monsters in the waters, Thou didst crush the heads of Leviathan; Thou didst give him as food for the creatures of the wilderness.
I think that here Leviathan is used as a name for all the Leviathans in the oceans, as I don't think that a single animal could normally and naturally have more than one head. So when God divided the Red Sea for the Israelites to walk through it, He also killed some of the sea-monsters, and their bodies washed up onto the shore with the dead Egyptians.
Psalm 104:24-26
O Lord, how many are Thy works! In wisdom Thou hast made them all; the Earth is full of Thy possessions. There is the sea, great and broad, in which are swarms without number, animals both small and great. There the ships move along, And the Leviathan, which Thou hast formed to sport in it.
Okay, here the Leviathan is named as a species of animal that plays and cavorts in the seas and oceans. I think about dolphins and otters and sharks and sailfish and other sea animals that seem to play and dance in the waters of the Earth. And it is named with the ships that ply the waves, as comparable in size to them.
Isaiah 27:1
In that Day the Lord will punish Leviathan the fleeing serpent, with his fierce and mighty sword, even Leviathan the twisted serpent; and He will kill the dragon who lives in the sea.
This is referring to the Day of the Lord, and Leviathan is still in this Earth, still twisting in the waters of the seas, waiting for King Jesus to slay him with the sword that proceeds out of His mouth: His Word. He will attempt to flee, but none will be able to evade His ultimate judgement.
Even so, come, Lord Jesus!
