Weighty importance, seriousness, or dignity.
Laughing and splashing each other, they failed to realize the gravity of their situation until the canoe was within twenty feet of the falls.
Although closely related to gravitas, gravity can apply to situations and problems as well as to people. Gravity in the physical sense is, of course, what gives us weight and holds us on the earth. But weight can also mean seriousness. Thus, gravity in the nonphysical sense can mean seriousness in a person's manner but also the seriousness or danger in a situation.