The following websites provide a range of online dictionaries.
Reference Desk: Dictionaries
This site gives you a range of online dictionaries for you to choose from.
This is like a 'dancing dictionary". Have lots of fun while you are learning the meanings of words.
There are 156 dictionaries and 19,317,398 words on this site!
Based on the same principle of Wikipedia
The Free Dictionary NEW
Much more than a dictionary, there are many daily insights provided to readers.