How to Use the Built-In Dictionary Lookup Shortcut on a Mac

When reading a dense academic paper, a technical manual, or a classic novel on your Mac, you will inevitably encounter words you do not immediately recognize. The standard workflow for most people is to highlight the word, copy it, open a new tab in Safari, navigate to Google, paste the word, and type “definition.”

This process breaks your concentration and pulls you completely out of your workflow. It is also entirely unnecessary. macOS has a powerful, system-wide dictionary built directly into the operating system that you can access instantly with a single keyboard shortcut or trackpad gesture, without ever opening a web browser.

This guide explains how to use the built-in dictionary “Look Up” feature on your Mac to define words instantly.

Method 1: The Three-Finger Tap (Trackpad)

If you use a MacBook or an Apple Magic Trackpad, this is the fastest and most seamless way to define a word.

1. Hover your mouse cursor directly over the word you want to define. You do not need to highlight or click it.
2. Simply tap the trackpad with three fingers simultaneously. (Do not press down to click; just tap the surface lightly).

A small, floating panel will instantly appear right next to your cursor displaying the full dictionary definition, pronunciation guide, and origin of the word. If the word is a known entity (like a famous person or a movie), it may also pull a brief summary from Wikipedia.

Note: If the three-finger tap does not work, it might be disabled in your settings. To enable it, go to System Settings > Trackpad > Point & Click and ensure Look up & data detectors is set to “Tap with three fingers.”

Method 2: The Keyboard Shortcut (Mouse Users)

If you use a standard desktop mouse or simply prefer keeping your hands on the keyboard, macOS has a dedicated shortcut for this feature.

1. Hover your mouse cursor over the word you want to define.
2. Press Command + Control + D on your keyboard.

The exact same floating dictionary panel will appear instantly.

Method 3: The Right-Click Menu

If you cannot remember the keyboard shortcut and do not have a trackpad, you can still access the dictionary faster than opening a web browser using the standard context menu.

1. Highlight the word you want to define.
2. Right-click (or Control-click) on the highlighted word.
3. From the drop-down menu, select Look Up “[Your Word]”.

How to Customise the Dictionary Sources

By default, macOS searches the New Oxford American Dictionary and Wikipedia. However, you can add foreign language dictionaries, thesauruses, or specialized glossaries to this Look Up panel.

1. Open the dedicated Dictionary app on your Mac (you can find it in your Applications folder or search for it using Spotlight).
2. In the top menu bar, click Dictionary > Settings (or Preferences).
3. A list of dozens of available dictionaries will appear. Simply check the boxes next to the sources you want to use (e.g., Oxford Thesaurus, Apple Dictionary, or French-English translation).

The next time you use the three-finger tap or keyboard shortcut, macOS will pull definitions from all your selected sources simultaneously, making it an incredibly powerful research tool.