Hilarious means extremely funny, the kind of funny that makes you laugh so hard your stomach hurts. When something is hilarious, it's laugh-out-loud, can't-catch-your-breath funny that produces uncontrollable laughter.

A hilarious movie might have you giggling through the whole thing. A hilarious story your friend tells at lunch might make milk come out of someone's nose. Your dad's attempt to dance like people do in video games might be absolutely hilarious to watch.

The word suggests something that produces real, uncontrollable laughter, not just a polite chuckle. A joke can be funny, but a hilarious joke has the whole class cracking up. Notice the difference: if something makes you smile, it's pleasant; if it makes you laugh, it's funny; if it makes you double over gasping for air, it's hilarious.

People's sense of what's hilarious varies wildly. What sends your best friend into fits of laughter might barely make your sister smile. Sometimes the most hilarious moments are the unexpected ones: someone sitting down and discovering the chair isn't there, or a pet doing something completely ridiculous.