This site is a great vocabulary builder , and for each question you answer correctly sponsors of the site donate 20 grains of rice to the United Nations to help end world hunger. It is both educational and socially commendable! For younger students, you can use this site to help teach dictionary skills. For older students, you can do what I did and connect the site throughout the curriculum. I asked the HAL students to find out how many grains are in a pound! Talk about some challenging math!
This is a great anchor activitiy for students to do when they've completed work early.