Google is no more displaying the dictionary link in search results, which until now were dispalyed as a link leading to a definition in the top blue bar, when you searched for a word in the dictionary. Google linked to dictionary.com until 2005, then it switched to the more comprehensive answers.com.
To find definitions using Google, you can use the define: operator. For e.g. just search for define:house and you'll get a lot of definitions from a variety of source, but not all of them are authoritative. Or subscribe to the Merriam-Webster OneBox to add a special search result with definitions.
Source:→ Google System