Apple's Word of the Day screensaver is a great way to casually boost your vocabulary.
The Mac has many brilliant screensavers, which you’ll find in System Preferences or by doing a Spotlight search for ‘screen savers’ and then opening the ‘Desktop & screen saver’ option.
To use the Word of the Day screensaver:
Go to System Preferences.
Choose Desktop & System Preferences.
Choose the Screen Saver tab.
Scroll to the bottom of the list and click Word of the Day.
Click Screen Saver Options to choose a language other than your default computer's language.
Click Show with clock if you'd also like to how the clock display along with the screen saver.