Stupendous means amazing or awesome. You just won a million dollars and are donating it to charity? That’s stupendous!
While you might think of stupid as a mean word for someone who isn’t smart, it can also mean senseless or stunned. If something stuns you so much that you are amazed, it is stupendous. Think of a stupendous performance or stupendous scenery. When something is big enough to astound, also use this word. The tower rose to a stupendous height. It would take a stupendous effort to improve your D in history to an A!