When recommending someone avoid rushing into an activity, we still say “Hold your horses.” This is a modern spelling of the idiom. As Wikipedia says
“Hold your hosses” (‘hoss’ being a US slang term for horse) appears in print that way many times from 1843 onwards… The first attested usage in the idiomatic meaning [came] from Picayune (New Orleans) in September 1844, “Oh, hold your hosses, Squire.”
The literal meaning is older:
In Book 23 of the Iliad, Homer writes “Hold your horses!” when referring to Antilochus driving like a maniac in a chariot race.
It seems strange that the idiom has survived the arrival of motorized vehicles, but there is a modern variation: cool your jets, which Stackexchange says originated in the US and was first quoted in a newspaper:
1973 Daily Tribune (Wisconsin Rapids) 29 Jan. 1/1 If you want to cool your jets, just step outside, where it will be about 10 degrees under cloudy skies.
The expression refers to revealing a secret, and Snopes says it originated from “. . .chicanery practiced upon those purchasing livestock.” An unscrupulous seller would swap a cat for a pig that had been purchased. The buyer wouldn’t know he had been duped until he returned home and “let the cat out of the bag.” The expression “Pig in a Poke” was posted earlier, and it had a reference to this expression.
Searching for the origin of this expression led me to two of my favorite sources. The Phrase Finder quoted Charles Earle Funk’s wonderful book, A Hog on Ice & Other Curious Expressions. “This may be jocular or serious; one is sometimes taken for a ride when he suffers nothing more than being kidded, made the butt of some joke. But in a sinister and the original sense the person taken for a ride rarely returns. The expression was of underworld origin, coined in the United States during the wave of criminality after World War I, when rival gangs of law-breakers waged warfare on each other. Anyone incurring the displeasure of a gang chieftain was likely to be invited to go for a ride in the car of the latter, ostensibly to talk matters over and clear up the misunderstanding. The victim rarely returned from such a trip. . . .”
Sources agree on the definition: something that quickly affects or becomes known by more and more people. Rumors, diseases, and memes can spread like wildfire. But only dictionary.com offered anything on the origin.
In the twelfth century the term “wildfire” referred to a skin disease (if it was highly contagious, the modern usage for disease sounds like it has a very old origin) and the “figurative sense is recorded from c.1300.” includes several historical examples, but all modern – for example, from The Messenger by Elizabeth Robins, 1920. News can fly and flee, as well as spread, like wildfire.
There are many parts of our history that should make us proud, but there are other examples that we should consider with shame. One of the later is how badly Chinese immigrants were treated when they were transported to the U.S. to do difficult and dangerous jobs such as building railroads in the 1800s. The expression explains that the Chinaman wanting justice had little “. . .or no chance at all, a completely hopeless prospect.” The Chinese immigrants worked for extremely low wages to perform difficult and often dangerous jobs and were prevented from testifying on their own behalf in court if violence was committed against them.
This expression is used to describe someone who begins supporting a political figure, sporting team, or idea only after it has become popular or successful. The internet tells me “bandwagon” had its origin in a book written by P.T. Barnum published in 1855. The expression is often used to describe those who are only attracted after it appears a campaign, team, or idea is a sure winner.
According to the Phrase Finder, this was originally a nautical term when berth was used to describe where a ship would be moored. Sailors were warned to keep a wide bearing to maintain sea room around a moored ship. Captain John Smith used a version of the term in 1626. “Watch bee vigilant to keepe your berth to the windward.” In 1829 Sir Walter Scott wrote “Giving the apparent phantom what seamen call a wide berth,” which led to the current meaning of maintaining a goodly distance.