You know that teacher who always has a goofy smile on his face and a bad pun for the kids? He's got a jocund personality, meaning he's merry and cheerful.
The word jocund came from the influence of two Latin words, jocundus, which means pleasant, and jocus, which is just what it sounds like: a joke. Usually the word is used to describe people, but not always. Say your family gets together every year for a big, merry barbecue — you could describe it as a jocund gathering, or a jocund weekend. It's a sort of old-fashioned word, though, so use it sparingly.