Is it ensure, insure, or assure?
humidity hu·mid·i·ty (hyōō-mĭd'ĭ-tē)
Dampness, especially of the air.
The amount of water vapor in the air. Humidity is measured in two ways: (1) Absolute humidity is the percentage of water vapor actually present in the air. (2) Relative humidity is the absolute humidity divided by the amount of water that could be present in the air. Relative humidity indicates the degree of comfort or discomfort one feels from the humidity, because it indicates the amount of perspiration that can evaporate from the skin.