Levity

n.
  1. The quality of weighing less than something else of equal bulk; relative lightness, especially as shown by rising through, or floating upon, a contiguous substance; buoyancy; -- opposed to gravity.
  2. Lack of gravity and earnestness in deportment or character; trifling gayety; frivolity; sportiveness; vanity.
  3. Lack of steadiness or constancy; disposition to change; fickleness; volatility.