Opulent is a word that you will hear a lot around rich people looking to show off. "Remember the opulent buffet at Carrie’s sweet sixteen? Sixteen chocolate cakes iced in gold leaf!"
If you want to remember that opulent is a word describing lavish displays of wealth, you can think of the word opal to help you remember it — opal being a rare gem. And if you are lucky enough to be able to afford opulence yourself, don’t describe it that way. The word contains connotations of pretentious. And gold leaf cake aside, who wants that?