Does anyone know of a good online game or website where we can introduce DD9 and DD7 to some new vocabulary? Nothing too wildly advanced, mind you.

We were reading A Wrinkle In Time together and the word agog came up, which neither daughter had ever heard of, so I had them guess at the definition and then we looked it up. Their guesses were surprisingly good and we decided we would do some vocab this summer. A Wrinkle In Time is a good start for them since it does have a lot of words that they will probably not know the definitions of, but I was hoping for something else for when we are done with the book.

I was initially thinking about signing up for a "word of the day" type email and I found something for that, but I'd really like to to find a game or website that delves more into the etymology of the words. I would like it to be more game-like and fun and not just words with definitions. Hopefully someone might have some suggestions for us.