To fulminate means to protest or complain about something loudly and angrily, often at great length. When your dad fulminates about the terrible traffic on the highway, he's expressing his frustration forcefully and dramatically, going on and on about how terrible the drivers are. When a principal fulminates against students running in the hallways, she delivers a stern, lengthy speech about the dangers and rule-breaking.

The word suggests more than ordinary complaining. Someone who fulminates doesn't just grumble quietly or shake their head in disapproval. They speak out boldly and passionately, like thunder rumbling across the sky. A coach might fulminate against poor sportsmanship after watching opposing players cheat. A teacher might fulminate about students turning in sloppy homework.

People often fulminate about or against whatever bothers them. The word carries a sense of righteous anger: someone who fulminates usually believes strongly that something is wrong and wants everyone to know about it. While the anger is real, there's often something slightly theatrical about fulminating, as if the person is performing their outrage on a stage for all to see.