Here is a fun article about the word with the opposite meaning of Schadenfreude - gluckschmerz. That is, it means to take pain in someone else's pleasure. While it is gaining popularity (as discussed in the article), as Goofy, I am sure, will say - it really isn't a word. Which brings us back to when is a word a word. For example, they brought up "selfie." That's a word now? Or "vape," which I hadn't actually heard of.
So - why is Gluckschmerz not a word, but Schadenfreude is then? They were developed similarly. Here is a Blog article about it. Interestingly, it mentions that epicaricacy is the English word for Schadenfreude.
We've been talking about what is a word almost since the inception of this board. This 2004 thread has what Aput (a UK linguist who was excellent) said is a "...a very, very sensible essay and I agree wholeheartedly with how it makes all those distinctions. That's the perfect linguistic treatment of the subject." It was posted by Bob. However, unfortunately after all this time the stupid link doesn't work. Bob, I am assuming you don't remember the name of the essay?
The article was a pdf on the University of Sussex site, entitled "What is a word?". Unfortunately they appear to have taken it down as a search of their site (Linguistics and English Language working papers) shows a defunct link which leads to a 'not found' message.
Build a man a fire and he's warm for a day. Set a man on fire and he's warm for the rest of his life.