Dictionary.com is a free website that offers a wide range of features. Obviously, the main service is to give definitions to words you look up. When you key in a word, you get a lot of useful information. Different meanings and usages will be presented, together with the pronunciation guide. One drawback of this guide is that you have to be familiar with the pronunciation symbols. You can also find out the origins of the word on the same page. More than that, you can find links to other specialized dictionaries which may have the same word.
What I really like about this online dictionary is that you can search for an idiomatic expression or slang and chances are, you will find it there. It also shows the meanings of different collocations for a particular verb. This way, if you are not really sure what you want, you are able to choose from a wide range of words.
From the main page, you can access an online bookstore, a thesaurus, an encyclopedia, feature articles, puzzles, and a translator. You can even make use of tools such as the http://Dictionary.com toolbar. If you need to look up a foreign word, there are links to foreign dictionaries as well. Do you want to...