dictionary service

Dont know of one built-in to Windows. I mostly use Sachio Search Toolbar for Firefox to do that sort of thing but it is no longer supported so I hesitate to recommend it. Another Firefox approach is to use the "Context Search" extension which allows you to add a limitless list of specialized search options to the Firefox search bar, and to the context menu.

If not using Firefox, and just want the Dictionary, you might consider one of these
Dictionary.com
Which allows high-lighting a word then clicking a button on the browser bookmarks toolbar.

IEspell comes with Wikipedia and Merriam Webster lookup - plus the the spell checking function.