As readers, we see too many of these. Writers, the editors of today are largely marketers, not manuscript correctors! Especially when it comes to historicals, you know far more about the period than they do. So, believing that no-one would commit these bloopers if they knew better, we will be building a glossary of terms that we all use every day, but which may or not belong in your manuscript.
Too many writers do not stop to say, "Is this a slang term, or is it one the Bronte sisters knew?" Anachronistic slang needs to be avoided like cliches. Cruise through here for the fun of it, and to remind yourself how recently some former slang has become acceptable English, and also to find some period words that may add considerably to your novel's atmosphere.
AWFUL, meaning very, great, bad, poorly done. This is one of many words that in the late 1800s were hauled into usage as superlatives. Before then, it means only "inspiring awe" as you will have heard it in older hymns. "He has an awful voice" is high praise before 1850!
BACK OUT, either for retreat or to fail to fulfill an obligation, as in "He backed out of the engagement." In 1864 a vulgarism.
BARONET, inheritable title, only invented in 1611 by James I of Great Britain. You can't have a medieval baronet.
BIRTH FATHER/MOTHER -- this was unheard of before the 1980s, when the movement began to consider adoption normal rather than making children feel stigmatized or alienated. Previously, such a person would have been called the father or the mother, the real father/mother, or the natural father/mother. The anthropological term would be genitor or genitrix, the person who biologically generated the child, as perhaps different from the pater or mater, the person whom society recognises as the "legal" parent.
BLUE, as in "feeling blue," meaning depressed, down-hearted, suffering ennui. This is jazz talk, and Emily Post (1922) considers it slang, but not unacceptable in polite society.
BOOZE, meaning alcoholic drink, derives from the Egyptian beer called "bouza." Egypt was an alien planet to Eupeans until Napoleon's invasion, so this will not have been used as a general slang term until enough British soldiers have been stationed there to have picked it up around the barracks and then brought it home: mid to late 1800s. Americans will have got it later yet.
CHECK OUT, meaning to inspect, investigate, look at, examine. Can be used no earlier than the late 1960s, and the 1970s is safer. In the middle 1960s, the phrase is still simply "check" as in "Check this cool set of wheels!"
DIP, as in chips and dip. The concept of dips, whether with pretzels, potato chips, crackers, or zucchini strips, is stated by the BH&G Encyclopedia of Cooking as having been an American invention of the late 1940s, popularized in the 1950s.
CHOW, meaning food. From the Chinese pidgin, "chow-chow" for food or eating. This seems not to have entered American military slang ("chow hall" "chow time") until the US had developed "old China hands" in the later 19th C, and more likely the early 20th C., though it may be acquired from immigrant coolies. Before then, soldiers usually refer to "grub" or like sailors to "mess," as in "mess hall" and "mess call," just like the Navy still does.
CUTE, meaning winsome, darling, appealing. Emily Post (1922) lists this as unacceptable slang. It had meant sharp, especially sharp dealings, like a gangster saying, "That's a cute idea."
FAKE, meaning false, imitation, fraud. Emily Post (1922) lists this as slang, but one which is approaching acceptability.
FIT, as in "feeling fit," meaning healthy, well, vigourous. This was still recognizably slang in 1922. Earlier characters should feel "hale."
GRAFTER, meaning a taker of graft, a dishonest or grasping politician. Considered vigourous, but still slang, in 1922.
GROUCH, meaning bad-tempered, ill-tempered, snappish, unpleasant. In 1922, this was not only slang, but it tended still to refer specifically to someone irritable from a hangover.
GYPSY, meaning a wanderer or vagabond, is a corruption of Egyptian, the supposed origin of the ethnic Gypsies. They only entered Germany and France in 1419, Italy before 1422, Paris in 1427, England before 1436, Spain in the mid-1400s, and overall are a Renaissance and modern phenomenon in Western Europe. In short, you will have no Gypsies at the French medieval fairs, and no other sorts of vagabonds being called gypsies. They only entered Eastern Europe from Turkey late in the previous century, being reported from Greece in 1398, though they may have been in Bulgaria in the 11th century.
HOOCH, meaning alcohol, came out of the American settlement of Alaska, originating as "hootchenoo." So it did not exist before 1870, would be restricted to Army men having done duty in Alaska and such until 1890, and only seems to have gotten popular in "the American vulgate" some while after that.
HUNCH, meaning an idea, suspicion, premonition. Emily Post (1922) lists this among slang words, but not one of the offensive ones.
MOVIES, meaning motion pictures. In 1922, this slang was only just acceptable.
NAG, meaning an unfit, infirm, decrepit or ill-bred horse. This is the modern meaning. The archaic meaning, used through the Middle Ages, Renaissance, and on into the early Modern periods, is non-pejorative: merely a light saddle horse. You might want to use the Middle English spelling, nagge, when you use it for the type.
PONY: first used in the English language in the mid-1600s, and then not common until the early 1800s. In the late 1700s, one could write of "small horses" in the Shetland Isles without anyone thinking it an odd way to describe Shetland ponies. It is from a French word for "foal." Any slang or dialectical use of "pony" like "pony up" is late 1800s or early 1900s.
RAPE, meaning forced sexual intercourse. You know how jumpy the Victorians were about any mention of sex, so if they used this word without blushing, you know it didn't have a sexual connotation! In fact, until this century it only meant "carrying away," as in Pope's mock-epic, "The Rape of the Lock," about stealing a lock of hair, or Bulfinch's reference to "The Rape of Helen" (she was, after all, completely willing, but she was carried away). In fact, the words "rapt" and "rapture" are only the past tense and a noun form of "rape." This structures like burn/burnt, keep/kept: rape/rapt, as in "She was rapt away by her imaginings." This is a real hair-tearer, because the reader cannot imagine any other meaning for this now very loaded word. Probably, you should just try to avoid using it in settings before 1900, at least in the mouths and thoughts of characters. The phrase usually used in the time used was that women "were outraged" or "were forced." Also, remember in your research that when a group is said to commit "rapine" in a 12th century source, they are referring to "carrying away" people, not sexually abusing them, as in "the vikings rapt away the monks."
ROYALS, meaning "royal family," did not exist before the 1980s. Even so, it means only the royal family, and a king "and his royals" cannot and does not mean the king and his court or the nobility or peerage as a whole, only to the royal family. Only an American with no sense of rank could commit such a faux pas. If you wish a lower class person to refer flippantly to the court or the king, try referring to him as "His Nobs" or "Their Almighty Nobs." It's closer in period.
TAXI, meaning a hired car. This is listed as barely acceptable slang by Emily Post (1922).
TERRIBLE, meaning bad, nasty, unfortunate, ill-done. Up into the late 1800s this meant "causing terror" as in "terrible swift sword." Someone who is a "terrible dresser" should be called instead a bad dresser or vulgar dresser, unless you mean that their choice of clothes inspires terror.
TIMING, meaning when something occurs. The phrase, "good/bad timing" and all its variations -- wonderful, lousy, execrable, etc. -- is a mechanical phrase, based on promulgation of reliable watches, and strongly attached to the development of revolvers, which have timing -- the intermeshing of parts to rotate the cylinder. Before 1900 it sounds odd, and before 1850 bizarre. Before 1800, it is completely out of place. Use punctuality, promptness, choice of time, opportunistic.
WHEELCHAIR -- In the 1895 Montgomery Wards catalog, there are "rolling chairs" with two large wheels in the back and two small ones in the front, only meant to be pushed; and there are "invalid chairs" with one or two small wheels in the back and two large wheels with handrails in the front for the person in the chair to operate. It is 1908 before we see "wheelchair," used provisionally in the Sears Catalog, and the preferred term is still "invalid chair." Only in the 1922 Montgomery Wards does the term "wheelchair" predominate. So your invalids or paraplegics of the 19th century in before will get around in invalid chairs, not wheelchairs -- at least in their own conversation and thoughts.
The Art of Conversation 1864
Bloomingdale Catalog, 1886
The Montgomery Ward Catalog, 1895
Sears, Roebuck Catalog, 1900
Sears, Roebuck Catalog, 1902
Sears, Roebuck Catalog, 1908
The Montgomery Ward Catalog, 1922
Emily Post, Etiquette 1922
Encyclopedia Americana, 1959
The Merriam Webster Unabridged Dictionary, 1968