Today’s topic: words that are experiencing definition drift, but aren’t yet fully unmoored from their original meaning. That means you can “misuse” them without most people realizing it, but some pedantic subset of readers/listeners will snicker up their sleeves at you.
Here are two prime offenders:
1) Nauseous. Most people think of this word as synonymous with “nauseated,” as in, “I’m feeling nauseous this morning.” What does it/did it actually mean? “Nauseating,” as in, “I passed a nauseous car accident on the way to work.” So every time someone says, “OMG, I’m so nauseous today!” the pedants might think, “with that kind of vocabulary, you sure are!”
2) Disinterested. Many people think of this word as synonymous with “uninterested,” but it actually means “unbiased.” This one isn’t as far gone as “nauseous,” so beware.
That’s all for now, but I’ll probably rinse and repeat as I think of new examples.
The Active Voice 
I’ve got a ‘sort of’ one! Succubus : )
I’ve seen it used in the context of someone being a drain or leaching off another – but a succubus is actually a supernatural demon that seduces you sexually, more a siren, let’ s say than a car that drains you of petrol money! Bloke version is an incubus. However where the use is partially correct, is that if a man has an encounter one too many times with a succubus, she could kill him or sap his health. The wikipedia entry is fascinating on this.
Viz your words – I’ll put my hand up and say i am guilty of ‘disinterested’!
Ah, interesting! So the more complex workings of the succubus get collapsed into something simpler, like a parasite or sponger. I bet that happens a lot: similarities between words lead to conflations of those words, and the nuance gets lost.
Which is why I know I need an editor. I think I know every word I use, but who the hell knows. Maybe after twenty or thirty more years of doing this I’ll be comfortable enough to trust myself. Definitely not now.
Hey, everyone has blind spots. Probably even editors. (Scary!)