The root of all evil is eall yfel

Here are 3 online games based on word origins:

Etymologic
"The toughest word game on the web"
Guess the language and root word for a set of 10 words. (It took me a bit to notice the answer and scores displayed at the top of the page after you click submit.)

Daily BuzzWord
Click on Daily Buzzword. For more words click Archive.
You're given the definition and how it's used and then have to answer a question that might be about the origin, or a synonym or ...

FakeOut!
Guess the real definition from a list. There aren't many words (click on More Words to access the archive) and you have to click on Fake Out link at the bottom of the page to move to the next word, but the words are challenging. (I'm not sure what inspired the grade ranges on the words. I think most adults would find them challenging.)