Other words, by sense
Select a word, or leave the caret in it, and choose Synonyms in the bubble or press ⇧F7Shift+F7. The thesaurus opens by the word, its meanings each with a short definition, the most common first: words for the same thing, more specific ones (ways to walk, kinds of house), broader ones, and opposites.
Every word comes already in the form of the one it replaces: “walked” offers “strolled”, “bigger” offers “larger”. Choose one and it takes the word’s place; ⌘ZCtrl+Z takes it back. A group of words it doesn’t know as a phrase can be looked up a word at a time, and its field looks up any other word.
It works offline, in scenes and on every page you write.
In Spanish
The Spanish thesaurus is Spanish’s own. Its meanings have no definitions, so they’re numbered, the everyday ones first, and it reads Spanish’s forms as the English one reads English’s: “caminaba” offers “andaba”, “mirándola” offers “observándola”.
Spelling
Words are checked as you write, in scenes, on pages, and in anything written at length, such as summaries and notes. A misspelled word gets a wavy underline, which waits until you’ve finished typing it. Right-click one for what you may have meant, or Add to Vocabulary so it’s never marked again, in any project. Settings lists your vocabulary, to add words or take them away.
The names and aliases of your characters and your world are never marked. Nothing is corrected as you type: you decide.
The dictionaries are part of the app (American or British English, or Spanish as Spain writes it), so checking never needs the internet, and what you write never leaves your computer.