Expanding Vocabulary

I am seeking to expand my vocabulary and wish to do it in a regimented environment; however, I am finding it difficult to procure a means by which to do that. Do any of you know of any computer programs that could aid me in this? I am specifically seeking something that would present with me random definitions and test me on them. Thank you for your time.

http://www.freerice.com/
A vocabulary-testing game.
For each answer you get right, they donate 20 grains of rice to a hunger program.

Sound good?

Awesome site, sir! I have donated 800 grains of rice thus far, having only missed a few. It appears as though my vocabulary isn't so bad after all, merely that I am unable to recall it for personal use.