See glossaries and definitions in Books on Mac
If you’re reading an interactive book that has a glossary, you can look up the glossary entries.
See a book’s glossary
In the Books app on your Mac, click Books (or another collection) in the sidebar.
Double-click an interactive book that has a glossary.
Choose View > Show Glossary.
If the book doesn’t have a glossary, the command is dimmed.
Click a glossary term.
See a word’s definition and other information
Control-click the word, then choose Look Up Selection. See Look up words.