Denim= De Nîmes (from the city of Nîmes)

Jeans = Gênes , the French weird for Genoa.

The cotton weave, indigo dyed cloth originated in Genoa, and in France the main production centre was Nîmes.

So 'denim jeans' is both a tautology and a contradiction

The "mast" in "mastodon" is the same one as in "mastectomy".

"The term "mastodon" comes from Greek roots: "mastos" meaning "breast" and "odon" meaning "tooth," referring to the nipple-like projections on the mammal's fossil molars. The name was coined by French naturalist Georges Cuvier in 1806."

In English, the words for many animals (chicken, cow, sheep, deer, pig) are derived from proto-germanic, while the word for their meat (poultry, beef, mutton, venison, pork) is French derived.

Bonus: A good chunk of river names are just "River" in the local language. So many River Rivers from newcomers adopting the river names, not knowing it just means "river"

The British insult "tow rag" or "toe rag", referring to a contemptible and worthless person, is named after the nautical precusor to toilet paper:

Back in the days of sailing ships, the sailors did not have toilet paper. What they did have were rags. Cloth rags known as "tow". After having completed their daily evacuations, sailors would engage in ablutions using a rag. This rag was then tied to a rope and dragged behind the ship in order to clean it (or them).

https://snowbirdofparadise.com/2020/04/02/the-tow-rag-explained/

You might be familiar with the radio term "roger." Per the FAA's Pilot/Controller Glossary, it means "I have received all of your last transmission. It should not be used to answer a question requiring a yes or no answer."

They want to make it VERY clear that roger does not mean "yes." So why do we use the word "roger" to mean "acknowledged"? Because Americans in World War II.

First of all, radio was still a fairly new warfighting tool in the 1940's. In a lot of cases, they still used Morse code tapped out by telegraphers on straight keys. Morse code was like the SMS of its day, it takes a long time to spell each letter out, so you end up with abbreviations, some of which really only make sense if you're familiar with Morse. For example, you know the radio practice of saying "over" and "out?" In morse code, you use K (-.-) to mean "over" and KN (-.- -.) to mean "out." There's an entire list of "Q codes", for example, you can tell someone to reduce their transmitter power by simply transmitting QRP (--.- .-. .--.). There's one that means "what's your barometric pressure?" because aviation. You'll still sometimes hear "What's QNH?" in aviation circles.

Most relevantly, a reply that simply means "I have received all of your last transmission" is simply abbreviated to R (.-.).

They also had AM voice mode radios. And now we get to talk about phonetic alphabets. We've all independently invented one at least once, talking to tech support on the phone and reading a serial number "One Three Four D as in Dog, Two, E as in Egg, Seven Eight one." Because a bunch of letters sound the same when saying them out loud. You might be familiar with the modern one used by NATO, also required by the aviation world via ICAO. Starts out Alpha Bravo Charlie Delta etc. R in the modern one is Romeo. But NATO formed well after WWII.

The phonetic alphabet used during WWII by English speaking nations went Able Baker Charlie Dog Easy Fox etc etc. Peter Queen Roger Sugar etc etc Xray Yoke Zebra.

So we say "Roger" because in WWII the Morse code abbreviation for "received" was R and the letter R would be pronounced "Roger" on an AM transmitter, and even though the phonetic alphabet has moved on, the word remains in use with a specific definition.

Barbecue comes from Spanish barbacoa which comes from Taino language used in the Caribbean region. Natives there invented barbecue, the Spanish took it to the old continent and it spread from there.

Chocolate comes from náhuatl language used by Mexica people. Xocoatl, from xoco 'sour' y atl 'water'.

Coach (as in bus) comes from Hungarian kocsi. They invented a type of horse pulled carriage which later gave the name to the coaches we know from westerns and then to busses and cars. Coche (car in Spanish) has the same etymology.

Admiral comes from Arabic "amīral". "Amir" means king, prince, chief, leader, and "al" is the definite article, in English "the" (compare algebra or alchemy).

So admiral means "leader of the", the Arabic for "leader of the sea", Amīr al-Baḥr, was too long to survive the whole game of telephone.

The word "standard," meaning "level of quality" or "rule" evolved from the physical battle flag on a pole, as in "standard bearer." So for things like standardized lengths of measurement, you could say "we follow the king's standard for what a foot is," which was a metaphor for following the king's rule on what that length was. That further stretched into a level of quality or conduct that needed to be achieved.

This might be obvious to some, but I only recently realized. A standard was originally a flag on a poll, meant to be visible across a battlefield as a direction for all to follow.

I don't think anyone has mentioned "helicopter" yet. It's not heli and copter like you might think. It's helico like helix meaning spiral and pter like pterodactyl meaning winged.

Floors in the Middle Ages were dirt covered with straw for insulation and other reasons.

Threshold = thresh (straw) + hold (a piece of wood across the front doorway to stop the thresh from spilling out)

This is a great question btw. ✌️

Buckaroo comes from the inability to pronounce/ the mispronunciation of the Spanish word for cowboy, Vaquero.

Copacetic -- it was just invented as a fake word to mean OK, all clear

Boondocks, meaning a remote place, entered English from the Tagalog word bundok, meaning mountain. American soldiers returning from occupying the Philippines introduced it in the early 20th century.

The word "nice" used to mean "stupid." It derives from the Latin "nescio" (translated: "I don't know") and carried over into old French. At some point, it came to be associated with generosity, the assumption being that someone stupid is too innocent or naive to be selfish.

It then got carried over into middle English, and the connotation for stupidity got dropped, making it so that the word meant "kind," as opposed to "stupidly kind"

Not a "common" term, but the word Neanderthal comes from the name of a river valley in Germany where neanderthals were first discovered. The valley in turn is named after a Calvinist hymn writer named Joachim Neander who often visited the valley and used its natural beauty as inspiration for his hymns. I find the unintentional synthesis of two ideas that many people would otherwise regard as incongruous to be beautiful in a weird way.

In the phrase "to get off scot-free", the word scot has nothing to do with Scotland or the Scottish. It's an Old English word meaning fine or penalty.

I once overheard a tour guide confidently tell a group of visitors to Edinburgh that the phrase was coined after one of the "grave robbers" Burke and Hare became a witness for the prosecution and was released. Burke and Hare were actually Irish, and they were murderers.

Snafu and Fubar are WW2 acronyms used as slang, there are many other acronyms in the same family, and new ones that have been added since.

Radar is also a WW2 acronym.