The crux of the matter, or, the etymology of "crucio"

[Carol]

I'm transferring this post from HPfGu because there's not much canon involved.

Carol earlier in <http://groups.yahoo.com/group/HPforGrownups/message/186462>:

<< "Crucio" *means* "I torture" and "Cruciatus" is a real Latin word meaning "torture" or "torment." The successful caster *must* want his victim to suffer unendurable agony, as Bellatrix knows well and as the name itself should be sufficient to inform us. (Even if we don't know Latin, we should see the etymological connection with "excruciating.") >>
Catlady responded:
How are these words connected with 'crux' meaning 'cross'? Are all the words meaning torture (except 'torture' itself, which comes from 'twist') derived from cruxification? Was the cross named 'instrument of torture' and then the + T X shape was named after the instrument of torture?

Carol again:
I deliberately left "crux" (cross) and "crucifixion" out of my post because the etymology is rather complicated. I can't find an etymology for the noun form, "crucifixion," but here's the etymology for the verb "crucify" from Merriam-Webster Online:

"Middle English crucifien, from Anglo-French crucifier, from Late Latin crucifigere" (fourteenth century)

Which takes us to "figere," the infinitive form of "figo" (fix or fasten), so "crucify" means "fasten to the cross."

Much earlier, in Roman times, "crux" had already taken on a secondary meaning, clearly related to crucifixion:

crux crucis f. [a cross]; hence [torment, trouble]; as a term of abuse, [gallows bird].

http://catholic.archives.nd.edu/cgi-bin/lookup.pl?stem=crux&ending=

The Latin word for "crucify" was the same as the word for "torture" or "torment," (crucio, cruciare). "Excruciate" is specifically derived from "cruciare" in this sense:

"Etymology:
    Latin excruciatus, past participle of excruciare, from ex- + cruciare to crucify, from cruc-, crux cross
Date:
    circa 1570

1: to inflict intense pain on: torture 2: to subject to intense mental distress"

Carol, betting that JKR knew full well all the etymological implications of the word she chose for her torture spell