Magnanimous behavior is noble, generous, or unselfish, and to exhibit magnanimity is to be this way. He showed great magnanimity in not pressing charges when I drove his car into the pond. "Accidents happen my friend," he said, and patted me on the back.
In Latin, magnus means "great": a magnate is a great man; a magnum is a great big bottle of champagne. Magnanimity is the generous greatness of spirit. When you are being the bigger person, you are behaving with magnanimity. "The supermodel grabbed the magnum of champagne, lifted it to her mouth and drained the bottle. With great magnanimity, her host smiled and offered her another."