Subject: Language Arts
I would use this site, MetaGlossary, as a tool for my students to use to search online for definitions. As an introduction to this site, I would make up a little quiz, about 10 questions, that they would have to look up words to find the definition for. Then they would have this resource to use in the classroom when they needed to find a definition. This site also offers links to sites where you can find more information on the topic requested. In addition, it has "related words" that they can click on to find more information on.
I am in early childhood, but there is no telling where I will end up getting a job and what grade that will be. There is far too much reading on this site for students in my age group, but I think this would be a great site to use in middle years and beyond.