Dictionary not working on macOS Catalina

After upgrading from El Capitan to Catalina you probably need to update the preferences for the Dictionary app.

Open Dictionary, click on its name in the menubar, select Preferences.

Check the boxes next to the Dictionaries and Thesauruses you want to use

and click and drag them into the order you want to see them, this should

force the mac to download and update your Dictionaries and Thesauruses.

You should see a progress bar at the bottom of the screen.

Have you tried restarting your mac in Safe Mode, then try opening Dictionary.

After you have done that restart normally and try the Dictionary app.

How to use safe mode on your Mac – Apple Support

Have you tried restarting your mac then.