Free on-line English dictionary

Kids Wordsmyth is a great visual dictionary that I learned about through Richard Byrne blog. 
It is a type of resource that I like to link to and feature prominently on this blog (useful webs for children, right side).

Students can search for words, hear them pronounced, read definitions and see illustrations of words as I said. Thus, when they don't understant the definition, the picture could help students grasp the description of the word.

Also, the dictionary is arranged in a virtual book with tabs for each letter of the alphabet.