Your longanimity is what keeps you calm and patient, even when you're running late on a crowded bus that's stuck in rush hour traffic.
Use the noun longanimity when you want an uncommon way to say "cool, calm, and collected." If you stay relaxed and smiling while you're waiting to get a driver's license or on hold with the cable company, you've got an admirable amount of longanimity. The Latin root is longanimitas, which means "long-suffering or patient" and comes from longus, "long," and animus, "spirit or mind."