This makes a lot of sense for a lot of queries and a perfect example are dictionary searches. Users may sometimes want to find out what a word means or see if their understanding is correct and they don't want to go through several steps just to get a quick glance at a definition.
Google has had a way of retrieving definitions directly via the "define:" operator. Typing "define," "definition" or "dictionary" also worked for most searches.
In these cases would provide an inline definition of the word and also a link to its dedicated dictionary page.
But the search engine has been expanding this feature and has started providing definitions for most single word queries containing terms that may not be overly common.
Now it's expanding on this as well with a new search option in the left sidebar, "Dictionary." Normally, these options are used to filter and restrict the search results, for example by date or by reading level.
With the Dictionary option, you actually get redirected to Google's dictionary search which retrieves definitions, synonyms, usage examples and similar info. It also retrieves search results from known dictionary websites, so, in a way it can still be considered a search page.
The new search option had been spotted in the wild in recent weeks. Google regularly tests new features and design changes with a few users before deciding which version to implement.
Now it seems that the Dictionary filter has been rolled out to everyone and is available under the "More search options" link.