Why do you need these Latin phrases? Well, like Latin teachers always say, Latin lives on in plenty of English words and phrases. But mostly, it's worth learning a bit of Latin because omnia dicta fortiori, si dicta Latina: everything sounds more impressive when said in Latin.
Ad hoc: Literally meaning "for this," it's generally used to mean improvised.
Ad infinitum (not to be confused with et cetera): "To infinity, without end."
Caveat emptor: "Let the buyer beware."
Citius altius fortius: "Faster, higher, stronger" - the motto of the modern Olympics.
Columbarium: A collective tomb in ancient Rome that was also used as a house for pigeons and doves.
Corpus christi: "The body of Christ."
Cuius est solum eius est usque ad coelum et ad inferos: "Whoever owns the land it is theirs up to the sky and down to the depths." The state of Kansas used this law in the 1970s to argue that airlines could not serve liquor when flying over Kansas, a dry state. "Kansas," Attorney General Vern Miller said, "goes all the way up and all the way down." (If that's true, Kansas can lay claim to, and prohibit drinking in, about 82,282 square miles of western China.)
Deus ex machina: "A god from the machine," usually referring to an awkward and contrived resolution to conflict. The phrase got its start from the plays of Euripides, in which a god was lowered down onto the stage via a mechanical crane to sort out intractable conflicts and confused plots.
Et ignotas animum dimittit in artes: "And he sent forth his spirit among the unknown arts." A beautiful quote from Ovid.
Id est: "That is," often abbreviated "i.e."
In medias res: "In the middle of things." Stories like Paradise Lost or The Odyssey or Sweet Valley High #17 begin in the middle.
Ipso facto: "By the very fact," i.e., "absolutely, regardless of circumstances."
Lupus est homo homini: "Man is wolf to man." No one knew this better than the Romans.
Magnum opus: Great work.
Nolo contendere: When you want to enter a plea of No contest" in as fancy a way as possible.
Opus Dei: "The work of God" or "An outsized villain in a bestselling novel."
Quod erat demonstrandum: "That which was to be demonstrated." Abbreviated QED, often the end of a mathematical proof.
Sic semper tyrannis: "Thus always to tyrants," the motto of Virginia and the
Sic transit gloria: "Glory fades," popularized by Max Fischer, founder, Rushmore Double-Team Dodgeball Society.
Sub poena: "Under penalty," as in "Do this or you're in trouble."
Tabula rasa: A "blank slate" - John Locke's description of the human mind without knowledge.
Veni, vidi, vici: "I came, I saw, I conquered," and the most oft-mispronounced Latin phrase in the world. It should be pronounced, WAY-nee, WEE-dee, WEE-kee.
From mental_floss' book Scatterbrained, published in Neatorama with permission.
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