It's no Vocabulary.com but it does help build comprehension.

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.