I regularly use the Mac’s Lookup feature to define key terms. Giving users the option to create their own dictionary entries would REALLY speed up the writing process for those who write in genres such as fantasy and sci-fi. Obviously, an individual can already do this by creating pages and linking to them, but adding those links is a bit time-consuming. Giving the user the option to invoke a hotkey and see a tiny pop-up with their brief description and pronunciation text is something I’d really love to see as I use a lot of strange terms and names that I’d love to easily reference without having to do the whole “switch to another note” process.
It may be an existing feature might do what you need well enough. Though it does depend upon naming items in the binder using the words you might be wishing to look up at a future time, that in practice shouldn’t be a problem for what you are describing. If you create an item in the binder describing a particular city in your novel’s world, you would want to use the name of the city in its title, and then right-clicking on that word in the future would give you an “Open…” hint at the top of the contextual menu to jump straight to the reference.
No need to use links in other words, though adding one instead of navigating would only require a minor modification in which contextual menu item you select.
If you do prefer a pop-up instead of navigating and then using the Back key (⌘[), then hold down the Option key when selecting the reference from the right-click menu.