How I Use It
I usually introduce Dictionary.com to my students as a reference tool. It's a good way of introducing students to the way a dictionary really works (roots, etymology, etc.). That said, it's really best as a reference. It's hard to use in any systematic way with word lists or anything like that. It replaces a dictionary well, and it also provides some fun challenges and games, but that's the extent of it.
I like the app and the challenging range of words, but the ads that fill the site are another reason that this is not a great classroom tool. Vocabulary.com still reigns supreme for me.