Risible means laughable or ridiculous, so absurd that it makes you want to laugh. When something is risible, it's so silly or preposterous that you can barely take it seriously.

If someone claims they can jump over the school building in a single bound, that's a risible boast. When a character in a story wears a risible costume, like a detective disguised so poorly that everyone recognizes him immediately, the disguise is laughably bad. A risible excuse is one so weak or far-fetched that it actually makes the situation funnier, like claiming your homework blew away in a tornado when there hasn't been wind in weeks.

It often carries a hint of scorn or disbelief along with the humor. Something risible strikes you as foolish enough to deserve laughter, because the absurdity is so extreme. Politicians sometimes call their opponents' plans risible when they think those ideas are too absurd to merit serious discussion.

Note that risible describes things that provoke laughter, while visible (which sounds similar) means able to be seen. A risible mistake is one so silly it makes people laugh; a visible mistake is one people can see.