Reading back through your notes and hit a word you're not sure of — a term you jotted in a hurry, a bit of jargon from something you clipped? Two ways to get its meaning without leaving the page.
Select a word or phrase and the floating format bar appears; click ✦ Explain. A small popover opens right there with a plain, one-breath definition written by your on-device AI — in context, so an ambiguous word is read the way you meant it. Click away to dismiss it. It is normally your local model doing the work, so nothing you select is sent anywhere. The exception is Bring your own model (see Local AI): with that on, Explain is one of the things you ask for, so the phrase and the sentence around it go to your provider. A page with a password on it is never explained either way. No model set up? The button tells you so rather than failing silently.
Prefer the real dictionary — Oxford, a thesaurus, Wikipedia, Apple's built-in sources? Right-click a selected word and choose Look Up "…". macOS's own Look Up panel opens with definitions, synonyms, and more. It's the system reference you already trust, one click from any note.
The two are complementary: Explain is a quick, contextual gloss from your AI; Look Up is the formal dictionary. Reach for whichever fits the moment.