Humidity is relative to the temperature and the dew point, if the temperature is near the dew point the humidity is going to be higher. There are two different ways to measure humidity either relative humidity which is the percentage of water that can be in the air. Or absolute humidity which is the amount of water in the air.
Heat index
The heat index takes in to consideration the humidity and the temperature this new temperature is what it actually would feel like.
Wind chill factor
The wind chill factor takes into consideration the wind speed and the temperature this can make it fell much colder.