Grandiloquent means using fancy, impressive-sounding words to make yourself or your ideas seem more important than they really are. Someone speaking in a grandiloquent way uses long, complicated words when simple ones would work better.

Imagine a student saying, “I shall endeavor to commence the implementation of my mathematical computations,” instead of just, “I'll start my math homework.” That's being grandiloquent: puffing up ordinary things with unnecessarily fancy language.

Politicians sometimes speak grandiloquently when they want to sound impressive without saying much. A grandiloquent speaker might use phrases like “utilize” instead of “use” or “substantial precipitation” instead of “heavy rain.”

Being grandiloquent is different from having a good vocabulary. When you know a precise word that expresses exactly what you mean, that's smart communication. But when you pile on fancy words just to show off or hide that you don't have much to say, that's grandiloquence. Mark Twain joked about this: “Don't use a five-dollar word when a fifty-cent word will do.”