See glossaries and definitions
If the book you’re reading was made for iBooks and has a glossary, you can look up glossary entries. You can also look up a word using the Dictionary app in macOS.
See the glossary: Choose View > Show Glossary. If the book doesn’t have a glossary, Show Glossary is dimmed.
To see the glossary entry, click a glossary term in a book.
See definitions: Double-click any word.
You can also select a word, choose More, then choose Look Up, Search Book, Search Web, or Search Wikipedia. For more information about looking up words in macOS, see Look up words.