Other forms: gravities
In physics, gravity is the natural force that causes things to fall toward the earth. The noun gravity can also mean seriousness or solemnity.
Someone who conducts themselves with an air of gravity is someone who takes what they are doing seriously. You might be amused to see a three year old serving her dolls tea with an air of gravity appropriate to the Queen of England. Gravity was borrowed through French from Latin gravitās, from gravis "heavy."