A recent legal blog post (here) on wind generators being given a permit to "take" (read, "strike dead") Bald Eagles had the headline that the eagles were "nonplussed." I had to look it up.
The prefix "non" usually means "not," but nonplussed without the "non" is nonsense. I'm confused. Actually, the Latin (non plus) does mean "no more to add." But there is no English word that describes a person's mental state as "plussed," as in perfectly clear. Got it?
That reminds me of several other confusing words I've noted over the years.
What's the difference between flammable and inflammable? Well, it turns out that inflammable comes from the Latin "to light on fire." In the 1920's the National Fire Protection Association thought that people were confusing inflammable (easy to catch fire) with nonflammable (not able to catch fire). Inconceivable! (not conceivable) That's bad. What to do? Invent a new word! They coined "flammable" and encouraged its use over inflammable. Both mean exactly the same thing, easy to catch fire.
When is the last time you heard of a gruntled worker wreaking havoc at their place of employment? It could happen, because gruntled is a word. No disrespect, but I do not think it means what you think it means.
Disgruntled means dissatisfied. The "dis" that prefixes "satisfied" means NOT satisfied, right? But the "dis" in front of gruntled does NOT mean mean NOT. Gruntled is an old form of "grumble." It does not mean "happy." The "dis" in front means "more." So, while a gruntled employee is a grumbler, a disgruntled employee is a real problem.
Want more examples of words that have negative connotations without corresponding positive meanings? See Grammar Girl's "Don't worry, be gruntled."