How to Look Up Definitions and Synonyms on Your Mac

You’ve run into a word you don’t know—or the one you’ve written five times needs a different option. Your Mac has a built-in Dictionary app that can help with both.

Quick answer: Open Dictionary, type a word in its search field, and choose Dictionary or Thesaurus to see the available results. You can also use Look Up from many apps without opening Dictionary first.

For this guide, we searched for an example word in the Mac Dictionary app and switched between its Dictionary and Thesaurus sources. The in-app Look Up shortcut is based on Apple’s instructions; we did not test it in every app. Available sources and the layout may differ with macOS and your settings.

Search in the Dictionary app

1. Open Dictionary on your Mac. If you’re not sure where it is, use Spotlight to search for Dictionary and open the app.
2. Click the search field and enter a word. Try serendipity as a harmless example.
3. Select a matching result if a list appears. Choose Dictionary for a definition or Thesaurus for related words, when those sources are available.
4. Read the entry in context. A synonym isn’t always interchangeable: check the examples and part of speech before swapping it into your sentence.

In the test, switching to the Thesaurus tab changed the entry to related words. Your results may vary depending on the dictionaries enabled on your Mac and the term you enter.

Look up a word without leaving your work

When you’re reading a webpage or working in an app, Apple’s documented method is to Control-click a word or phrase and choose Look Up from the shortcut menu. Some apps require you to select the text first. The window can show a short definition; if available, choose more for the full entry or Open in Dictionary for the app.

Apple also documents a three-finger tap when that gesture is enabled in Trackpad settings, or a force click on supported trackpads configured for Look Up. Those gestures depend on your hardware and settings; the Dictionary app search is a straightforward fallback.

If the result isn’t there

• Check the spelling. Try a simpler form of the word, or select another result in the list.
• Try another source. Select All, Dictionary, or Thesaurus if shown. Some sources may not contain the term.
• Check enabled dictionaries. Apple says you can use Configure Dictionaries in the Look Up window to open Dictionary settings and select sources. Availability and download requirements can vary.
• No Look Up option? Select the text before Control-clicking, or open Dictionary and type the word. Menus differ between apps.

Dictionary is useful for a quick definition or a better word choice. For a claim that depends on specialized or current information, check a relevant source rather than treating a dictionary entry as the whole answer.

For another built-in Mac tool, see how to convert and resize images in Preview.