What is the difference, if there even is one between the heat index?

Question

and the humidity? I always thought the 2 words were interchangeable. But I am starting to wonder now. Both words refer to how hot it can feel on any given day.

Answer 1

Heat index is a number that describes the body's response to heat and humidity. The higher the number the harder it is for your body to cool down. It is sort of how hot it would feel with low humidity.

Humidity tells how much water vapor in the air. Relative humidity is the ratio of the actual amount of water vapor in the air to the amount that would saturate the air. Knowing the humidity tells you nothing about the temperature. You can have a high relative humidity in either hot or cold conditions.