Q: What do vocabulary and world hunger have in common?
A: FreeRice.com
At FreeRice.com you will find a fun game designed to improve your vocabulary. But there is a twist - for every correct answer Free Rice donates 20 grains of rice to help end world hunger.
Here is an excerpt from the Free Rice About page that explains their mission:

About FreeRice

FreeRice is a sister site of the world poverty site, Poverty.com.

FreeRice has two goals:

1. Provide English vocabulary to everyone for free.
2. Help end world hunger by providing rice to hungry people for free.

This is made possible by the sponsors who advertise on this site.

Whether you are CEO of a large corporation or a street child in a poor country, improving your vocabulary can improve your life. It is a great investment in yourself.

Perhaps even greater is the investment your donated rice makes in hungry human beings, enabling them to function and be productive. Somewhere in the world, a person is eating rice that you helped provide. Thank you.

You can now do something as simple as playing a game to help end world hunger.