Computers, Laptops & Tablets Apple How to Use the Dictionary and Thesaurus in macOS Mail Find Definitions for Words Instantly by Heinz Tschabitscher Writer A former freelance contributor who has reviewed hundreds of email programs and services since 1997. our editorial process Heinz Tschabitscher Updated on June 03, 2020 Apple Macs iPad Tweet Share Email You can access both a dictionary and thesaurus while composing messages in the macOS Mail app. The operating system comes included with The New Oxford American Dictionary and The Oxford American Writer's Thesaurus, as well as other dictionaries. All can be easily accessed within macOS Mail. The same process for looking up words in the Mail app applies to any text-based app, including web browsers, word processors, and reading apps. JGI/Jamie Grill/Blend Images/Getty Access Dictionary and Thesaurus in macOS Mail Here's how to instantly access the dictionary and thesaurus in macOS Mail: With the Mail app open, place the mouse cursor over or within the word you would like to look up. Tap with three fingers on the trackpad. Alternatively, press Command+Ctrl+D on your keyboard. A window will appear listing a definition of the word, as well as a Thesaurus entry with corresponding synonyms. You can choose from a host of other options from the definition window. Select Open in Dictionary to open the word entry in the macOS Dictionary app. At the bottom of the window, you can scroll through a host of entries in other categories, including Wikipedia entries, movies, or other knowledges sources. Select Configure Dictionaries to choose from a list of dictionaries to include in the app as well as the pop-up definition.