A “dialog” (also spelled “dialogue”, should you be playing Scrabble and need the extra points) is a conversation, generally between two people. It’s from Greek, and made up of “dia” (through) and “logos” (to speak). It was a single word even in Greek though: “dialogos.” It entered Latin “dialogus” and Old French “dialogue,” where it picked up the “ue” at the end, which it brought with it to English in about the 1100s.
But what if there you are having a nice conversation with one person and someone else joins in? Apparently that didn’t started happening in English until around 1500, because it was around then that they discovered they needed another word: “trialogue.” That’s just what you think: a conversation among three people. It isn’t used much, which is why the silent “ue” at the end hasn’t yet worn away. Moreover, it’s a word that’s likely based on a mistake: they probably thought that the “di” in dialog was part of the root and meant “two,” so why not just replace it with “tri”, meaning three? Except the “di” in “dialog” never meant “two” at all. Besides, by that logic we’d need words for a conversation among four (“quadralogue”), five (“pentalogue”) and many people (“multilogue”). Or possibly we already have a word that fits: “noise”. But the number of people doesn’t really affect what we call the conversation. Probably because it’s the act of discussing that’s at the heart of “dialog,” and the number of participants isn’t particularly relevant.
That’s not always the case; we have enumerating words for two people working together (duo), three (trio), and on up to “octet” (eight, especially used in music). In those cases the number of participants is the whole point, so there’s a specific word that focuses on it.
Now, when it comes to railroad locomotives — and it comes to them only because I found a 1956 book Quiz on Railroads and Railroading — the arrangement of wheels was considered quite important. This was particularly true for steam locomotives, which had a combination of small wheels that do nothing but support the unit, and very large wheels, which are the ones delivering power to propel the train. One of the advantages diesel-electric locomotives offered when they were developed was traction — every wheel could have its own electric motor, so the locomotive could have a larger number of smaller “drive wheels” compared to a steam version. With more drive wheels, you get more traction, so even if the overall power is equivalent, a diesel-electric locomotive can pull a heavier train. But back to the arrangement of wheels. Steam locomotives were traditionally described by their wheel arrangements, so a “4-6-2” locomotive had 4 small wheels, 6 large drive wheels, then two more small wheels.
For some reason every combination of wheel arrangements was also named, so (at least in the US) a little 0-4-0 locomotive was a “switcher”, a 2-6-0 was a “Mogul,” a 4-6-2 was a “Pacific,” and not to be left out, a 4-4-2 was an “Atlantic”. Apparently the most gargantuan steam locomotive, a 4-12-2, was called a “Union Pacific” because that was the only railroad that had one. Since they also had the Rocky Mountains to cope with, that might be why.
Some locomotive types were named for places, such as the 2-6-6-6 “Allegheny” and the 2-8-4 “Berkshire.” Some were named after implements (the 4-8-8-2 “Mallet”) or animals (the 4-10-0 “Mastodon”), but probably the best name landed on the 2-10-0 “Decapod.” There seems to have been only one exception to the naming convention: the 4-6-0 was simply the “Ten Wheel.” Maybe there just wasn’t enough dialog about what to call that one.
