This morning, while I was home for lunch, Jennifer asked me what I thought the sources were for these two J.K. Rowling neologisms. We talked about it a little — I’d had some passing thoughts, but hadn’t looked into them any more closely than that, and I said I would. She suggested a blog post. And so, voici, voilà ...
The fact that the incantation for both spells ends in —mens immediately suggests the Latin mens “mind”, which is also perfectly consistent with their intended functions. But Wikipedia also suggested an echo of the combining form —mancy, which they defined as “divination”, as in necromancy or bibliomancy. That’s a good thought, but of course, that element (from Greek —μαντία) derives from the same source as Latin mens, Greek μένος “mind”. As a side note, this root also gives us mantis, as in praying mantis, in which mantis actually means “prophet” (cf. Greek μαντις “seer”), and mantic, an uncommon adjective meaning “prophetic”. Sybill Trelawney would be so delighted! :)
So that’s the last element down. What about the first?
In “legilimency”, the element legili— unequivocally incorporates the meaning of Latin legere “to read”, but it’s so much fresher than that hackneyed old metaphor, “reading minds”. This verb has secondary uses, too, of “to collect, to choose” (unmentioned by Wikipedia), both of which enrich the meaning still further and seem appropriate to how Rowling has described the process and experience of legilimency.
Then, according to Wikipedia again, occlu— in “occlumency” comes from the Latin occludere “to close up, to block off” (cf. Modern English occlude). That certainly makes sense — though where has the –d– gone? In any case, they’re on the right track, but I would like to submit an alternate or additional possibility as well. The Latin occulere (no missing phonemes here!) means “to conceal, to cover up, to hide”, which sounds just as appropriate, if not more so. It’s also the source for our Modern English word occult (from the past participle occultus “concealed”), which is a pretty compelling bonus, if you ask me.
So there you have it: the likely etymologies for “occlumency” and “legilimency”. It’s just too bad we can’t actually perform these thaumaturgic “sleights of mind” in real life, isn’t it?