Orphaned Etymology

The inverse of Hold Your Hippogriffs and Oh My Gods, it's when someone uses an expression which could not possibly have come into use, due to Speculative Fiction history preventing the etymology from taking place, making it an instance of Inexplicable Cultural Ties. "Jeez" or variants are the most commonly seen words which invoke this trope. Another form of this trope happens in Historical Fiction and the like, with words and phrases that aren't supposed to have come into use yet. This is most often used with words which are Newer Than They Think, or when people in the year 700 BC refer to the present time as "700 BC".

When played straight, this is often an aspect of the Translation Convention, in that the phrase is uttered for the viewer's benefit, rather than the characters'. Ways to defy this trope include Hold Your Hippogriffs, Oh My Gods, or You Mean "Xmas".

Depending on how deeply and pedantically you're willing to go, this is pretty much unavoidable whenever you're using modern-human language in a time or setting that isn't modern Earth. Because of the way language evolves, it's hard to come out with a sentence or two that doesn't somehow reference some real-life history.

In written works, this trope only applies to characters' dialogue, or when the work is written as a character reflecting on the events. As the author is from Earth, they can use the words the characters cannot.

Another variant of this trope is used for humor, such as yelling out "Jesus Christ!" in front of the real Jesus, who will usually assume that He is being addressed.

Anime

 * In the English dub of Inuyasha, there's an episode where he remarks, "We've all got our own cross to bear." This is set before Christianity was introduced to Japan.
 * Fullmetal Alchemist: As far as it's shown, there's nothing like a benevolent monotheist deity — there's the jerkass god, Truth, and there's Father, who's kind of like Satan. However, Greed does a See You in Hell to his family and Buccaneer references Fluffy Cloud Heaven. Then again, people are shown to believe in a variety of religions, so Your Mileage May Vary.
 * Christianity is shown to have existed in the 2003 anime version, but this doesn't justify the examples in Fullmetal Alchemist: Brotherhood or the manga.
 * In Sonic X, there is a character called 'Black Narcissus' despite his race never having visited Earth and in fact existing in a whole other universe! (also, Sonic X's earth doesn't appear to have the same countries anyway...)

Comic Books

 * A Dub Induced Plot Hole in the Spanish version of an Asterix comic book: A character sneezes, and Asterix says "Bless you!" — which in this context is translated to Spanish as "¡Jesús!" This raised the question for Spanish readers of how could Asterix say that in the year 50 B.C.

Film

 * In Mel Brooks' History of the World Part One, Comicus says "Jesus" in exasperation during The Last Supper, causing Jesus to answer, "Yes?" assuming that Comicus was addressing him.
 * The 1980 Flash Gordon movie has the War Rocket Ajax as part of Ming's fleet. Ajax, of course, was a famous Greek hero, and Ming has never heard of Earth before the start of the movie.
 * Battlefield Earth has the alien Psychlos refer to Euclidean geometry, though this might have been Translation Convention.

Literature
"The dragon passed like an express train, turned a somersault, and burst over Bywater with a defeaning explosion. "
 * One of the earlier Discworld books references gypsies, which is kind of a problem, since there's no Egypt in the universe to derive that name— the equivalent is called Djelibeybi. So, if there are Roma on the Disc, they should probably be nicknamed Jelibeybs or something like that.
 * In Witches Abroad, there's a reference to a christening. In Carpe Jugulum and Nanny Ogg's Cookbook, this has been replaced with Naming Ceremony.
 * Parodied in the Assassins' Guild Diary which uses the orphaned word "byzantine" ... in explaining that the politics of the Komplezian Empire were the origins of the modern Morporkian word "complex".
 * In the introduction to The Discworld Companion, Pratchett says that a fantasy author may start out trying to avoid references to things like "Toledo steel", but sooner or later will just look up from their keyboard, mutter "what the hell" and give up.
 * In the Dragonriders of Pern series, Pernese still say "jays" and "by all that's holy" despite having Outgrown Such Silly Superstitions. Mildly justified in that they might just be holdover expressions from the original Terran colonists.
 * Deliberately averted in The Lord of the Rings. Tolkien, as a linguist, did his best to remove and replace modern English words that derived from languages other than English. For example, "pipe weed" is clearly tobacco, but isn't called such because the word "tobacco" comes from a language native to the Caribbean.
 * But not totally averted, since "potato" and its derivative "tater" come from the Taino word "batata".
 * Tolkien even states even the names used for the characters aren't "really" their names, but rather our cultural equivalent. For example, Frodo's "real name" in untranslated Westron (Common speech) is "Maura Labingi".
 * And yet, we have the interesting fact that in chapter 1, a dragon is compared not only to a train, but an express train:

"324 B.C., Jan. 6 - Note: Find out what "B.C." stands for."
 * In His Dark Materials, Lyra refers to uranium mines, but a later chapter refers to "the other five planets", indicating that Uranus hasn't been discovered in her world. (In our world, uranium was named after Uranus because they were discovered around the same time.)
 * Parodied in Dave Barry's Complete Guide to Guys, where one of the entries in Alexander the Great's diary reads:

"Ben: Even a duck has to be taught to swim. Luke: What's a duck?"
 * In an interview Christopher Paolini, author of the Inheritance Cycle, mentioned this problem, specificially citing "backpedaled" as a word he couldn't use. He used it anyway.
 * George R.R. Martin also slips once in a while, and uses words like "damask" in a world with no city named Damascus, "turkey" (the fowl) where there is no country of the same name, or "chequy" when the setting's analogue to chess is cyvasse.
 * In The Ringworld Throne, a native of Ringworld refers to how the irritable chieftain of the Grass Giants might "go off like a volcano" if he finds out about something, which is puzzling because Ringworld has no volcanic activity.
 * In Septimus Heap, Septimus uses "Rats!", which is kinda problematic in a world with talking rats.
 * The novelization of Star Wars: A New Hope includes a small dialogue in which Obi-Wan Kenobi is musing about training Luke.


 * This is a bit of an aversion, since several of the Star Wars tie-ins around the time it came out seemed to be written under the assumption that earth creatures did in fact exist in the galaxy far far away. The reason Luke doesn't know what a duck is because he lives on a desert world.
 * Eventually, ducks are introduced into canon.


 * The Kingkiller Chronicle plays with this in some weird ways. There are several fictional dead and in-use languages in its world, so a Translation Convention is assumed. Then you get things like the word 'vintage'. In our world, it comes from Latin by way of French, referring to wine (vin, vino, vinum, etc...), but it's not any more out of place than any other English word in fantasy. However, in the Four Corners there is no Orphaned Etymology, because the word vintage is derived from the country of Vintas, which happens to produce fine wine.

Live-Action TV

 * Thanks to Throw It In, Battlestar Galactica's Colonel Tigh exclaims "Jesus!" in a polytheistic society that's never heard of Abrahamic religions.
 * Dinosaurs uses the B.C. timeline. Lampshaded in the first episode when Robbie asks why the dates go backward. "I mean, what are we counting down for? What are we waiting for?"
 * History Bites also uses this trope in the episode focusing on Ancient Rome. Also lampshaded as the news anchors repeatedly say "whatever B.C. means."

Video Games

 * In Star Fox 64, Falco, rather infamously, sarcastically calls Fox McCloud "Einstein" if you shoot him. When a reader of Nintendo Power magazine sent in a letter questioning how could a being from another galaxy know about Albert Einstein, the editors' response was, "Because the game's creators are from this galaxy, Einstein."
 * Falco says not only, "Einstein," but also, "Jeez Laweez, what's that?" He really loves this trope.
 * In Adam Cadre's Shrapnel, a character fighting in the Civil War calls another "Einstein" --
 * In Dragon Quest, this is used a lot. It is even Lampshaded in Dragon Quest V, where the phrase "proud as Punch" is used and the Hero's daughter wonders what Punch was proud about.
 * In Skies of Arcadia, the only kind of pirate in the 'verse is explicitly called a "sky" pirate, despite the lack of need for differentiation.
 * Dates in Chrono Trigger use BC and AD, even though Jesus Christ does not appear to exist in the game's universe.

Webcomics
"Alt Text: Hamlet has to say "record scratch" because records aren't invented yet so you can't make the sound otherwise, HOW IS THIS NOT OBVIOUS"
 * Exiern, a High Fantasy world with no relation to Earth, much less Japan, apparently has Yaoi Porn, mentioned by name.
 * and Band-aids.
 * and Hallmark cards although at least the characters have the good grace to admit they don't know exactly what they are.
 * According to Dinosaur Comics' summary of the play, Hamlet said, "Record scratch! Say WHAAAAAT?" when he found out how his father died.

Western Animation

 * In the animated The Return of the King, Samwise's response to Gollum's final attack is a very animated "Gooood help us!"
 * The Flintstones apparently live in the United States and celebrate Christmas. See the Wild Mass Guessing page for different interpretations...

Real Life

 * Surprisingly, there are actual pre-Christian Roman coins marked with years "BC." Current speculation is that were issued to commemorate a particular battle (in Latin, bellus) against a person or at a place whose name began with "C."