The define command on Google shows you the definitions for your query from different sources like Wikipedia, Answers.com etc. For “Define:query” search, Google used to show a separate page with just the definitions from different sources. But now the definitions also show up on the main search results.
As you type any query on Google, a list of the suggestions for the term shows up. This makes it easier and faster to search for anything. Besides you also get an idea of the related search queries. Google suggest has been integrated with Google Chrome and Firefox as well. Besides Google Suggest, Yahoo and Bing also show you the suggestions by simply populating the related and most searched terms. But if you want something more, here are some handy tools.
Google gives a lot more options for filtering your search results. Like if you want to look for the definition or meaning of a certain word, you need not go to dictionary.com and search for the word. You can get your meaning with the query, “define:word” in Google. Or you can find all the pages in a site with the query, “site:yoursite.com”. You can also get desired results by modifying the Google Query URL that it returns after a query.