Wordnik
Wordnik is the world’s biggest online English dictionary, by number of words. Wordnik shows definitions from multiple sources, so you can see as many different takes on a word’s meaning as possible.
Lexipedia – Where Words Have Meaning
Lexipedia is an online visual semantic network with dictionary and thesaurus reference site. Lexipedia presents words with their semantic relationships displayed in an animated visual word web.
Lingro – Dictionary for Websites
Lingro refers to itself as the coolest dictionary known to hombre.
When you visit the website, you can paste the address of another website into the top search field, then it will allow you to click on words you don’t know the meaning of, and Lingro will define the words.
Word Hippo
Word Hippo is a cute thesaurus/dictionary/word rhyming for younger learners. It asks the question “What’s another word for” at the top of the screen and children can type their sought-after word into the search space. The search at the top of the screen changes based on the tab. When on the Antonyms tab, it will ask “What is an antonym for ___?”
This site could also be useful with older students working on rhyming and poetry in Language Arts class.