If you’re “nonplussed”, you’re either stuck, in a thinking sort of way, or you’re confused or perplexed by something. But does that suggest that if you figure something out, you ought to consider yourself “plussed?”
Nope. “Nonplussed” is a word that came from a phrase, and when you disassemble the phrase it loses all of its meaning, so “plussed” isn’t a thing at all. “Nonplussed” comes from the Latin phrase “non plus” (not much of a stretch there), which means “no more.” So “nonplussed” suggests that your stuckness or confusion is terminal; you just can’t go any further. That’s why being “plussed” would make no sense; you’d be saying that you’re “more”.
I ended up nonplussed when I tried to find out where the phrase “rule of thumb” came from. The most common origin story is just a myth: it suggests that in the 17th century, English law held that it was acceptable for a man to beat his wife, but only with a stick that was no thicker than his thumb. This is nonsense; there was never any such law. But on the other hand, nobody seems to know where “rule of thumb” really came from. The best guess is probably that your thumb, which is in most cases difficult to misplace, is (ahem) a handy measuring tool in many trades, particularly since the average distance from the end of your thumb to the first joint is around an inch. (Hmmm, where do you suppose inches came from?)
It’s a good rule of thumb that if you hear that a word is an acronym, check it out because unless it’s a NEW word, it’s probably not an acronym at all. The words “acme” and “posh” are sometimes described as acronyms — but they’re not. “Posh”, in the acronym story, is supposed to come from the days when it was relatively common to travel by ship between England and India. The best cabins would be on the side of the ship sheltered from the sun, so the richest travelers got them — and the way that worked was when you were going “out” (toward India) you’d want a cabin on the left side (“port,” in nautical lingo), and on the way home you’d want to be on the right (“starboard”). The acronym theory, then, is that the best and most expensive cabins were “Port Out, Starboard Home”. However, it turns out that nobody who ever worked on or around those steamships ever heard of this. Instead, “posh” probably comes from the Romany word “posh”, which meant “half”. Besides that, Romany was widely spoken in the London underworld back in the old days, and in Romany “posh-houri” was slang for “half pence.” From there the term got shortened to simply “posh,” and the meaning got lengthened to simply “money.” After that, it progressed to its current meaning of “expensive” or “elite.”
As for “acme,” while there seems to be a myth that it’s an acronym, that myth doesn’t have a consistent message about what the acronym is supposed to stand for. It probably comes from the fairly common practice in the late 19th and early 20th centuries for companies to include “Acme” in their name to try to appear first in alphabetical listings (such as those newfangled telephone directories). It wasn’t invented by Warner Brothers, where Wile E. Coyote would order gadgets from the “Acme” company in his battle with the Road Runner. By the 1960s, companies naming themselves “Acme” was already enough of a joke that the cartoon folks just latched onto it as a pretty funny idea. “Acme” really comes from the Greek word “akme,” which means the top, or highest part of something, such as a mountain. Probably because of its Greek origin, its pronunciation and spelling are unusual for English. That’s probably where the myth originated. If it isn’t, I guess the rule of thumb would suggest we’re just nonplussed.
