Use Word's Thesaurus to Find a Better Term

When you're working on a Word document and you want to look up a better word to use, double-click the word to mark it, and then press the Shift + F7 keys.Research pane

This will open Word's Thesaurus on the right side of the document (known as the Research pane), and a list of suggested synonyms will appear.  If you click on the word in the list you want to use, you'll get a dropdown menu where you can click "insert" to have Word substitute the new word in place of the old one.