Jormungand literally means »large staff« in Old Norse; compare Gandalf, a name which comes from the reckoning of the dwarfs in Völuspá and means »staff-elf«; that is, an elf that does magic. (This is incidentally one of several indications that an »elf«, in Norse myth, means neither more nor less than a dwarf; Snorre Sturlasson's division of the elves into ljósalfar and dókkalfar is much younger in origin, in no wise attested in Viking-age sources and almost certainly a pollution from the myths of the Irish, who had a significant effect on the culture of Iceland.)
In the present context a »staff« is a circumlocution for a snake; it is not, however — and I want to stress this — a kenning, which denotes a poetic metaphor, not just any Old Norse verbal imagery whatever. The point being, »Jormungand« means »Large Snake«. As has been previously remarked, Viking nomenclature was pretty direct for the most part.
Although the Midgård Serpent bites its tail, it is unlikely that it is meant to symbolize eternity in the way of an ouroboros; rather, the orbit of the serpent is meant to delineate the limits of the Earth, and for this it must encircle the whole disc of the world. The world must end somewhere; the image of the encircling serpent shows this place. It is needful therefore that it should connect to itself; for there are no gaps in the utter limit of Earth.
Jormungand's ongoing battle with Thor is an instance of the probably best-attested, most clearly proven motif that is Proto-Indo-European in origin, The Thunder God Fights The Dragon. This is a pattern of literally the highest antiquity known anywhere, to anyone; it predates by at least two thousand years the first we hear of Ptah, of Amun, of Sobek and Ra. It is barely more than a glyph, a gesture, a single character; but it is drawn in bedrock. Much speculation has been spilled, and many have spoken much nonsense, on the topic of PIE myth and religion, with »reconstructions« so tenuous as to be sheer fantasy; in cases like this I find it best to maintain the most acute skepticism about any claim; but the case of the thunder god and the dragon, much like the motif of The World, Carved From A Man Named Twin, meets even these stringent standards. Both of these we see in places as far afield from one another as Norway and India; both have a hard nucleus from which various tales have clearly been built up, rather than one version being »a good story« imported complete by strange and circuitous ways into the other, far-off land.
No, it is old; it is old beyond the reckoning of man. When you look at the Midgård Serpent, you do gaze upon the far and very limits of that world in which we live.