The noun risibility describes a wonderful quality in a person — the tendency to laugh often and easily.
You're forgiven for thinking this word means "an ability to rise." In fact, it means "readiness to laugh." You might remark on the risibility of your giggly little cousin. The etymology of risibility is somewhat obscured by the conjugation of its Latin root, ridere, which means "to laugh," but which also gives us deride and ridiculous.