Known among friends and family as a competent amateur etymologist and word-maven, I was recently challenged to explain the origins of the word henge, if I could. Some friends of my father-in-law had recently visited England and taken the usual obligatory guided tour of Stonehenge. During the tour, their crackerjack guide told them, “we’re not really sure what henge means.” Hrmph! I certainly wouldn’t have been satisfied with that explanation — in fact, being told “we don’t know” where a word comes from, why, it’s enough to make me come unhenged ... (Sorry, I just couldn’t restrain myself. ;)
Well, to begin with, henge, by itself, isn’t really a proper word at all. Or rather, it has only become a word through a process called back formation, but it wasn’t originally an independent word. But that, I suppose, is beside the point. What we really want to know is: what does the henge element in Stonehenge mean?
We find the earliest occurrence of Stonehenge in the writings of Henry of Huntingdon in the early twelfth century, in the form Stanhenges.  There are two theories regarding the meaning of the word. And either — or both — may hold the answer we’re looking for.
The first theory operates on the observation that many of the standing stones resemble mystical doorways. Doorways, of course, are composed of lintels, jambs — and hinges. Aha! Any evidence? Why yes! We have Middle English henge, hengel “hinge”  (with cognates Middle High German hengel, Middle Low German and Middle Dutch henge), and deriving from Old English hón, hangian “to hang, suspend”  (with cognates Old Norse hengja, Middle Low German hengen, Old High German hengan, henchman), and the clearly related hengen “hanging”, and “a gibbet, gallows, cross” . So, according to this, the more common interpretation, Stonehenge means something like “stone-hinge”. Sounds perfectly reasonable, doesn’t it? After all, look at the picture above: the stones certainly do resembles doorways.
The second theory is a little more interesting. According to it, Stonehenge may actually be the Stone(s) of Hengest, the semi-lengendary conquerer of Britain. This is an appealing proposition, but is there any evidence for it? Indeed there may be. Not long after Henry of Huntingdon, Geoffrey of Monmouth described Stonehenge as a “monument erected in the reign of Aurelius Ambrosius, King of Britain, in order to commemorate the slaughter of the Britons by Hengist” . Hensleigh Wedgwood also sets out the case for this possibility — as well as discussing the argument for henge “hinge”, inter alia, and offering several interesting specimens from the literary and historical record mentioning Stonehenge — in a pointed essay, “On the Etymology of the word Stonehenge” .
It must be noted that the “Stone(s) of Hengest” interpretation is definitely the minority opinion (perhaps mere folk etymology), but I like it. And it would certainly have appealed to Tolkien, who made clever use of the Hengest legend in the backdrop of his own fiction.  So, where does that leave us? We have two theories, and one, or both, of these etymological explanations may be correct (and both are certainly plausible). But “we’re not really sure what it means”? Please, you just aren’t trying!
 “Antiquarian and Literary Intelligence.” The Gentleman’s Magazine and Historical Review, December 1864: 717-58, p. 741.
 Stratmann, Francis Henry. A Middle English Dictionary. New ed. by Henry Bradley. Oxford: Oxford University Press, 1891, p. 337. (The entry Stán-henge also appears in this dictionary, with the straightforward definition “Stonehenge”, see p. 573.)
 Bosworth, Joseph. An Anglo-Saxon Dictionary. Ed. and enlarged by T. Northcote Toller. Oxford: Oxford University Press, 1898, pp. 510, 551.
 Ibid., p. 527.
 “Antiquarian and Literary Intelligence”, p. 741.
 Wedgwood, Hensleigh. “On the Etymology of the word Stonehenge.” Proceedings of the Philological Society Vol. VI, No. 130 (February 25, 1853): 31-35.
 See for example Smol, Anna. “History, Anglo-Saxon.” In The J.R.R. Tolkien Encyclopedia: Scholarship and Critical Assessment. Ed. Michael D.C. Drout. New York: Routledge, 2007: 274-7, p. 275.