Instructions courtesy of @chancelionheart:
Access the Settings menu by clicking the Options icon in the upper-right corner of the browser window. It is the icon with three horizontal lines stacked on top of each other. Click on “Settings” near the bottom of the Options menu.
Under the “Search” heading in the Settings menu, click the "Manage search engines" button.
At the bottom of the Search Engines window that comes up, enter the following: Name: Use whatever you like (I used "Webster's Revised 1913+1928 Dictionary") Keyword: Also whatever you like, I just use 'd' for easy access. Url: http://machaut.uchicago.edu/?resource=Webster%27s&word=%s&use1913=on&use1828=on (replaces the search term with %s, what google chrome uses for the query)
Now, you can search the dictionary from any new tab by typing in your keyword, a space, then the word.