macOS Sierra: Look up words
You can quickly look up the definition of a word or phrase while working in apps or browsing webpages. If Spotlight Suggestions are enabled in Spotlight preferences, you may see information about related locations, music, or movies, and you can click links to get directions or watch a movie trailer, for example.
Look up a word: Control-click the word or phrase (in some apps you may need to select it first), then choose Look Up from the shortcut menu. Or tap the word or phrase with three fingers (if the gesture is selected in Trackpad preferences).
If your trackpad supports force click, you can set the Look Up gesture to use that instead of a tap. (To force click, press firmly until you feel a deeper click.)
The dictionary definitions shown vary, based on the sources available in Dictionary preferences. You can open the Dictionary app using Launchpad in the Dock.