I heard about this web site today.
http://www.freerice.com/index.phpThe concept is simple. They ask you to match a word with its definition. (Multiple choice, four choices.) For every one you get right, they will donate ten grains of rice to feed the hungry. (Doesn't sound like much, but so far they have donated MILLIONS of grains of rice.) It's an easy way to help feed the hungry, improve your vocabulary, and have fun. (Who pays for it? The folks who run advertisements on the site, which are easy to ignore.)
I get to about "Level 43" on the vocabulary test before I start making mistakes. Even after that, I can often make an educated guess. It's interesting to see what words you know without knowing you know them, you know?
After the computer finds your starting level with a few beginning questions (I start at level 40), you go up a level by getting three answers in a row correct. Miss one and you go back down. The highest possible level is 50. I have never gotten higher than level 47. At that point, I'm just guessing at words I have never seen before.
Give it a try!